LIBRARY 

THE  UNIVERSITY 
OF  CALIFORNIA 

SANTA  BARBARA 

PRESENTED  BY 
MRS.  MACKINLEY  HELM 


FRANCIS  W.  SEVER 


77 


GRAY'S   BOTANICAL   TEXT-BOOK. 

VOLUME  II. 
PHYSIOLOGICAL   BOTANY. 


Copyright,  1885, 
BY  GBOHGB  LINCOLN  GOODALB. 


LIBKAtt  t 

UNIVERSITY  OF 

SANTA  BARBARA 


PREFACE   TO   THE   SEEIES. 


THE  first  edition  of  the  Botanical  Text-Book  was  pub- 
lished in  the  year  1842,  the  fifth  in  1857.  Each  edition 
has  been  in  good  part  rewritten,  — the  present  one  entirely 
so,  —  and  the  compass  of  the  work  is  now  extended.  More 
elementary  works  than  this,  such  as  the  writer's  Lessons 
in  Botany  (which  contains  all  that  is  necessary  to  the  prac- 
tical study  of  systematic  Phaenogamous  Botany  by  means 
of  Manuals  and  local  Floras),  are  best  adapted  to  the 
needs  of  the  young  beginner,  and  of  those  who  do  not 
intend  to  study  Botany  comprehensively  and  thoroughly. 
The  present  treatise  is  intended  to  serve  as  a  text-book 
for  the  higher  and  completer  instruction.  To  secure  the 
requisite  fulness  of  treatment  of  the  whole  range  of  sub- 
jects, it  has  been  decided  to  divide  the  work  into  distinct 
volumes,  each  a  treatise  by  itself,  which  may  be  indepen- 
dently used,  while  the  whole  will  compose  a  comprehen- 
sive botanical  course.  The  volume  on  the  Structural  and 
Morphological  Botany  of  Phsenogamous  Plants  properly 
comes  first.  It  should  thoroughly  equip  a  botanist  for  the 
scientific  prosecution  of  Systematic  Botany,  and  furnish 
needful  preparation  to  those  who  proceed  to  the  study  of 
Vegetable  Physiology  and  Anatomy,  and  to  the  wide  and 
varied  department  of  Cryptogamic  Botany. 


Vi  PREFACE. 

The  volume  upon  Physiological  Botany  (Vegetable  His- 
tology and  Physiology)  has  been  prepared  by  the  writer's 
colleague,  Professor  GOODALE. 

The  Introduction  to  Cryptogamous  Botany,  both  struc- 
tural and  systematic,  is  assigned  to  the  writer's  colleague, 
Professor  FAELOW. 

A  fourth  volume,  a  sketch  of  the  Natural  Orders  of 
Phaenogamous  Plants,  and  of  their  special  Morphology, 
Classification,  Distribution,  Products,  etc.,  will  be  needed 
to  complete  the  series:  this  the  writer  may  rather  hope 
than  expect  himself  to  draw  up. 

ASA  GRAY 

HERBABIUM  OF  HABVARD  UNIVERSITY, 
CAMBRIDGE. 


' 


PREFACE  TO  VOLUME   II. 


THE  present  volume  is  devoted  to  a  consideration  of 
the  microscopic  structure,  the  development,  and  the  func- 
tions of  flowering  plants ;  that  is,  to  their  Vegetable  His- 
tology, Organogeny,  and  Physiology.  In  the  first  volume 
of  the  Botanical  Text-Book  these  topics  were  treated  only 
incidentally,  or  in  an  elementary  manner,  as  an  introduc- 
tion to  Morphology. 

Cryptogams,  or  flowerless  plants,  are  treated  in  this 
volume  only  so  far  as  their  study  may  throw  light  on 
certain  features  of  the  anatomy  and  physiology  of  Phseno- 
gams.  The  simple  structure  of  many  of  the  flowerless 
plants,  especially  of  those  of  the  lower  grades,  makes  them 
suitable  objects  in  which  to  investigate  numerous  phe- 
nomena of  vegetable  nutrition,  growth,  and  reproduction, 
and  they  have  been  extensively  employed  as  convenient 
material  for  this  purpose.  Reference  must  therefore  be 
made  in  the  present  treatise  to  some  of  the  more  important 
results. 

Vegetable  Histology  treats  of  the  minute  anatomy  of 
plants.  A  knowledge  of  its  leading  facts  is  indispensable 
to  a  clear  understanding  of  Vegetable  Physiology,  and 
their  presentation  must  needs  precede  any  satisfactory 
examination  of  the  latter.  The  technique  of  Vegetable 
Histology  requires  special  treatment,  and  therefore  con- 


vjii  PKBFACE. 

siderable  space  has  been  devoted  to  its  appliances  and 
methods.  This  special  treatment  has  been  supplemented 
by  a  series  of  practical  exercises  which  the  student  is 
urged  to  perform  in  the  order  designated.  It  will  be 
seen  that  in  some  cases  several  examples  are  suggested  : 
the  beginner  is  advised  to  examine  thoroughly  at  least 
one  of  the  examples  under  each  head. 

Organogeny,  the  study  of  nascent  organs,  occupies  much 
of  the  middle  ground  between  Histology,  Morphology,  and 
Physiology.  The  means  by  which  it  is  investigated  are 
those  of  Histology,  but  its  answers  are  given  to  Mor- 
phology. For  convenience,  the  study  of  the  development 
of  each  organ  of  the  plant  is  made  to  precede  the  examina- 
tion of  its  mature  state. 

Vegetable  Physiology  concerns  itself  with  the  life  of 
plants.  The  appliances  of  which  it  makes  use  are  taken 
chiefly  from  Physics  and  Chemistry,  and  facility  in  their 
employment  demands  some  practical  acquaintance  with 
those  departments.  To  one  who  has  worked  systemati- 
cally in  a  physical  and  chemical  laboratory,  experimental 
vegetable  physiology  presents  little  difficulty.  To  aid  the 
work  of  students  whose  opportunities  for  experimenting 
in  Physics  and  Chemistry  have  been  slight,  a  series  of 
practical  exercises  in  Experimental  Physiology  has  been 
added.  The  appliances  selected  for  these  examples  are 
not  complicated  or  expensive,  and  it  is  hoped  that  teachers 
and  students  alike  may  find  their  employment  practica- 
ble. The  Praxis  embodies  in  compendious  and  conven- 
ient form  the  directions  which  have  been  employed  by 
the  author  in  his  classes. 

The  illustrations  of  tissues  and  of  apparatus  have  been 
taken  from  many  sources.  They  have  been  selected  with 


PREFACE.  tt 

reference  to  the  special  needs  of  those  students  to  whom 
the  larger  works  and  the  current  journals  are  not  easily 
accessible.  The  same  rule  has  been  largely  followed  in 
the  treatment  of  citations  from  authorities.  Where  it  has 
been  possible  to  do  so  without  too  great  sacrifice  of 
space,  the  phraseology  of  the  original  reference  has  been 
given. 

In  the  preparation  of  this  volume  the  author  has  had  at 
many  steps  the  wise  counsel  of  his  teacher  and  associate, 
Professor  ASA  GRAY,  to  whom  he  wishes  to  make  his 
grateful  acknowledgments. 

In  the  proof-reading,  verification  of  references,  and  In- 
dex, Mr.  W.  W.  NOLEN,  Assistant  in  Biology,  has  rendered 
aid  of  great  value.  His  painstaking  and  good  judgment 
have  lightened  in  every  way  a  formidable  and  burdensome 
task. 

GEORGE  LINCOLN  GOODALE. 

BOTANIC  GARDEN  OF  HARVARD  UNIVERSITY, 
CAMBRIDGE,  MASS.,  August,  1&86. 


CONTENTS. 


PART  I. 

INTRODUCTION. 
HISTOLOGICAL   APPLIANCES. 

Microscopes 1 

Dissecting  Instruments 2 

Media  and  Reagents 4 

Staining  Agents 15 

Mounting-media 20 

CHAPTER    I. 

THE  VEGETABLE  CELL  IN  GENERAL:  ITS  STRUCTURE, 
COMPOSITION,    AND    PRINCIPAL   CONTENTS. 

Protoplasm ...  26 

The  Cell-wall 29 

Cellulose 31 

Modifications  of  the  Cell-wall 34 

Plastids 40 

Protein  Granules 44 

Starch 47 

Inulin 60 

Cell-sap 61 

Crystals 62 

CHAPTER    II. 

CELLS    IN   THEIR   MODIFICATIONS   AND    KINDS,    AND  THE 
TISSUES  THEY  COMPOSE. 

Typical  and  Transformed  Cells .  66 

PARENCHYMA 60 

Parenchyma  proper 60 

Epidermis 64 

Epidermal  Cells 66 

Trichomes 68 

StomaU 70 

Cork     .  74 


X1i  CONTENTS. 

PAOK 

PBOSENCHYMA 76 

Prosenchyraa  proper 77 

Woody  Fibres 

Tracheids 

Tracheae,  or  Ducts 84 

Liber-fibres 87 

CRIBROSE-CELLS 91 

LATEX-CELLS 94 

Eeceptacles  for  Secretions 97 

Intercellular  Spaces 99 


CHAPTER    III. 

MINUTE   STRUCTURE   AND   DEVELOPMENT  OF    THE    ROOT, 
STEM,  AND  LEAF  OF  PILENOGAMOUS  PLANTS. 

The  Systems  of  Tissues    .    . ' 102 

Structure  of  a  Fibro-vascular  Bundle 103 

THE  ROOT 106 

Primary  Structure 106 

The  Root-cap .107 

The  Piliferous  Layer 108 

The  Central  Cylinder 110 

Secondary  Structure 112 

THE  STEM .  !  118 

Primary  Structure 119 

The  Epidermis t  119 

Primary  Cortex 119 

Primary  Bundles <  120 


Pith 


11M 


Medullary  Rays 124 

Course  of  the  Bundles .126 

Secondary  Structure !    136 

Of  Monocotyledons 

Of  Dicotyledons 

Changes  by  Growth 

Anomalous  Stems ,00 

Spring  and  Autumn  Wood 

Annual  Layers 

Color  of  Wood ] 

Preservation  of  Wood   . 

Density 

Bark 

Secondary  Liber    .    .    . 

cork ;  ;  ; 

Injuries  of  the  Stem  .... 
Lenticels    .    .    . 

*•"•• '.'.::' 


CONTENTS.  Xlli 

PAGE 

Rudimentary  and  Transformed  Branches 163 

Stems  of  Vascular  Cryptogams 164 

Stems  of  Mosses 164 

THE  LEAF 156 

Development 165 

Bundles 166 

Parenchyma 168 

Epidermis 161 

Fall  of  the  Leaf 162 

Leaves  of  Cryptogams 164 


CHAPTER    IV. 

MINUTE  STRUCTURE  AND  DEVELOPMENT  OF  THE  FLOWER, 
FRUIT,  AND  SEED. 

THE  FLOWER 166 

Preparation  of  Material  for  the  Study  of  its  Development ....  166 

Stages  ,in  its  Formation 168 

Tissue  Systems  of  the  Flower 170 

Development  of  the  Stamens 171 

Style,  Stigma,  and  Ovary 172 

Distribution  of  Fibro-vascular  Bundles  in  Simple  Pistils 173 

Distribution  of  Fibro-vascular  Bundles  in  Compound  Pistils  ...  173 

Formation  of  the  Ovule 176 

THE  FECIT 176 

Its  Structure  .  .  . 176 

Its  Coloring-matters 177 

THE  SEED ,178 

Structure  of  the  Seed-coat  and  its  Appendages 178 

Nucleus  of  the  Seed  7~  . 181 

Food  Materials  and  Protein  Granules  in  Seeds  .  .  182 


CHAPTER    V. 
PHYSIOLOGICAL  CLASSIFICATION  OF  TISSUES. 

DIVISION  OF  LABOR  IN  THE  PLANT 185 

Work  of  the  Plant  Organism 185 

Organs  and  their  Classification 186 

Haberlandt's  Classification  of  Organs 187 

MECHANICS  OF  TISSUES 188 

Strength  of  Tissues 190 

Stereom  and  Mestom 192 


CONTENTS. 


PART    II. 

CHAPTER  VI. 
PROTOPLASM  AND  ITS  RELATIONS  TO  ITS  SURROUNDINGS. 

PAGE 

Occurrence  of  Protoplasm 

Chemical  and  Physical  Properties  of  Protoplasm   ...  ™ 

Protoplasmic  Movements '    201 

Relations  of  Protoplasm  to  Heat 

ToLight 

To  Electricity 

To  Mechanical  Irritation 

To  Gravitation 

To  Moisture ^ 

To  Various  Gases f 

Structure  of  Protoplasm 2 

Continuity  of  Protoplasm 2 

Relations  of  the  Cell-wall  to  Protoplasm 218 

Historical  Note  regarding  Protoplasm 219 

CHAPTER  VH. 
DIFFUSION,  OSMOSIS,  AND  ABSORPTION  OF  LIQUIDS. 

DIFFUSION  AND  OSMOSIS 221 

Diffusion  of  Liquids 221 

Rate  of  Diffusion 222 

Osmosis 224 

Precipitation-membranes 226 

Traube'sCell 226 

Pfeffer's  Apparatus  for  Osmosis 226 

ABSORPTION  OF  LIQUIDS  THROUGH  ROOTS 280 

Root-hairs 231 

Extent  of  Root-systems 232 

Adhesion  of  Soil  to  Roots 233 

Do  Roots  go  in  Search  of  Food  ? 286 

CHAPTER  Vin. 

SOILS,  ASH  CONSTITUENTS,  AND  WATER-CULTURE. 

Amount  of  Water  and  of  Ash  in  Plants 236 

SOILS '.'..'...    287 

Formation  of  Soils .237 


CONTENTS.  XV 

FACE 

Classification  of  Soils 238 

Absorption  and  Retention  of  Moisture  by  Soils 239 

Chemical  Absorption  by  Soils 243 

Condensation  of  Gases  by  Soils 244 

Root-absorption  of  Saline  Matters  from  Soils 244 

Temperature  of  Soils 245 

Effects  of  Roots  upon  Soils 246 

ASH  CONSTITUENTS  OF  PLANTS 246 

Amount  and  Distribution 246 

Composition 247 

WATER-CULTURE 248 

Apparatus 249 

Nutrient  Solutions 250 

Method  of  Practice 251 

OFFICE  OF  THE  DIFFERENT  ASH  CONSTITUENTS 262 

Potassium 252 

Calcium  and  Magnesium 253 

Phosphorus 263 

Iron 264 

Chlorine 264 

Sulphur 265 

Sodium 255 

Rarer  Constituents 255 


CHAPTER  EX. 

TRANSFER  OF  WATER  THROUGH  THE  PLANT. 

THE  RELATIONS  OF  WATER  TO  TISSUES 267 

Transfer  of  Water  in  Woody  Plants 268 

Determination  of  the  Path  and  Rate  of  Transfer 259 

Rate  of  Ascent  of  Water  in  Stems 261 

Effect,  upon  Transfer  of  Water,  of  Exposing  a  Cut  Surface  to  the  Air  263 

Pressure  and  Bleeding 264 

Exudation  of  Water  from  Uninjured  Parts  of  Plants 267 

TRANSPIRATION 268 

Stomata 268 

Mechanism 269 

Relations  to  External  Influences 270 

Amount  of  Water  given  off  in  Transpiration 271 

Transpiration  compared  with  Evaporation  proper 276 

Effect  of  Moisture  in  the  Air  upon  Transpiration 275 

Effect  of  the  Soil  upon  Transpiration 276 

Relations  of  Temperature  to  Transpiration 277 

Effect  upon  Transpiration  of  Light 277 

Of  different  Rays  of  the  Spectrum 278 

Of  Mechanical  Shock 278 

Relation  of  Age  of  Leaves  to  Transpiration 279 


.  CONTENTS. 

PAGB 

279 
Relation  of  Transpiration  to  Absorption     .    .    -  ^ 

Adaptations  of  Plants  to  Dry  Climates   .    .  • 

Chief  Effects  of  Transpiration  upon  the  Plant     .         .    -     -    •    - 
Influence  of  Transpiration  upon  Amount  of  Moisture  m  the  Air  ,         SHI 
Effect  of  Transpiration  upon  the  Soil     .    •    •     •  283 

Do  Leaves  absorb  Aqueous  Vapor? 


CHAPTER  X. 
ASSIMILATION. 

APPROPRIATION  OF  CARBON,  OR  ASSIMILATION  PROPER  .    .    , 

Conditions  of  Assimilation 

Assimilating  System  of  the  Plant ~~ 

Chlorophyll 

Origin  of  the  Granules 

Occurrence  of  the  Granules * 

Structure  of  the  Granules 

The  Chlorophyll  Pigment,  and  its  Extraction **> 

Spectrum  of  Chlorophyll 

Fluorescence  of  Chlorophyll 2 

Plants  devoid  of  Chlorophyll 2 

"Colored"  Plants 29* 

Etiolation 2 

Chlorosis 2 

Autumnal  Changes  of  Color 297 

Chlorophyll  in  Evergreen  Leaves 298 

The  Raw  Materials  required  for  Assimilation,  and  their  Reception 

by  the  Assimilating  Organs 299 

Absorption  of  Carbonic  Acid  by  Water  Plants 299 

Absorption  of  Carbonic  Acid  by  Land  Plants 300 

Diffusion  of  Gases 801 

Passage  of  Gases  through  Epidermis  free  from  Stomata 302 

Passage  of  Gases  through  Stomata 308 

Composition  of  the  Atmosphere 803 

Practical  Study  of  Assimilation 306 

Energy 307 

Classification  of  the  Rays  of  the  Spectrum 308 

The  Depth  to  which  Light  can  penetrate  Green  Tissues 809 

Quality  of  Light  which  penetrates  the  Tissues  of  a  Leaf      ....    309 

Effect  of  Colored  Light  upon  Assimilation 310 

Measurement  of  the  Amount  of  Assimilation 312 

Engelmann's  Method 314 

Effect  of  Artificial  Light  upon  Assimilation 316 

Relations  of  Temperature  to  Assimilation 316 

Effect  upon  Assimilation  of  Variations  in  the  Amount  of  Carbonic 

Acid  furnished  the  Plant 818 


CONTENTS.  XV11 

PAGE 

Ratio  of  the  Oxygen  evolved  by  Plants  to  that  of  the  Carbonic  Acid 

decomposed 319 

What  are  the  Products  of  Assimilation  proper? 320 

First  Visible  Product  of  Assimilation 821 

Formic  Aldehyde  Hypothesis 822 

Pringsheim's  Views  in  regard  to  the  First  Product  of  Assimilation    .  322 

Early  History  of  Assimilation 323 

APPROPRIATION  OF  NITROGEN 325 

Amount  of  Nitrogen  in  Plants 325 

Sources  of  Nitrogen  furnished  to  Plants 327 

Nitrogen  Compounds  in  the  Atmosphere 331 

Nitrogen  Compounds  in  Rain-water 331 

Office  of  the  Atmosphere  in  the  Formation  and  Distribution  of  Nitro- 
gen Compounds 332 

Products  of  the  Decomposition  of  Animal  and  Vegetable  Matter  .     .  333 

Natural  and  Artificial  Fertilizers 834 

Synthesis  of  Albuminous  Matters  in  the  Plant 336 

APPROPRIATION  OF  SULPHUR 336 

APPROPRIATION  OF  ORGANIC  MATTERS 337 

Humus-plants,  or  Saprophytes 337 

Parasites 838 

Insectivorous  or  Carnivorous  Plants 338 

Drosera  rotundifolia 339 

Dionaea  muscipula 342 

Aldrovanda 344 

Drosophyllum 345 

Roridula 345 

Byblis 346 

Pinguicula 346 

Utricularia 846 

Genlisea 346 

Sarracenia 847 

Darlingtonia 849 

Nepenthes 349 

Dipsacus,  or  Teasel 860 

Epiphytes,  or  Air-plants 362 

CHAPTER  XI. 

CHANGES  OF  ORGANIC  MATTER  IN  THE  PLANT. 

TRANSMUTATION,  OR  METASTASIS 854 

Utilization  of  Food 354 

For  Supply  of  Energy  for  Work 356 

For  Repair  of  Waste 365 

For  Construction  of  New  Parts 365 

Assimilation  proper  compared  with  Respiration 356 

Course  of  Transfer  of  the  Assimilated  Matters  in  the  Plant ....  366 


xviii 

Classification  of  the  Principal  Organic  Products 367 

Products  free  from  Nitrogen '    ^ 

Carbohydrates 360 

Vegetable  Acids 3QQ 

Fats,  or  Glycerides 861 

Certain  Astringents [    y® 

Glucosides '     ggg 

Ethereal  Oils.    . 

Resins  and  Balsams 

Products  containing  Nitrogen 

Albumin-like  Matters '    2M. 

Asparagin 

Alkaloids 

Unorganized  Ferments 

RESPIRATION 

Measurement  of  Respiration * 

Plants  in  Dwelling-houses «L_ 

Relations  of  the  Carbonic  Acid  given  off  in  Respiration  to  the  Oxy- 
gen absorbed  

Influence  of  Temperature  and  Light  upon  Respiratiou « 

Resting  State 

Respiration  accompanied  by  an  Evolution  of  Heat 370 

Intramolecular  Respiration 87° 


CHAPTER  XII. 

VEGETABLE  GROWTH. 

Nature  of  Growth 373 

Cell-division 374 

In  the  Development  of  Stomata     .    , 376 

In  Cambium 377 

In  the  Development  of  Pollen-grains 379 

In  Plant-hairs 380 

Directions  in  which  the  new  Cell-wall  may  be  laid  down 380 

Growth  of  the  Cell-wall 382 

Measurement  of  Growth 383 

Conditions  necessary  for  Growth 384 

Relations  of  Growth  to  Temperature 386 

To  Light 887 

To  Supply  of  Oxygen 888 

Periodical  Changes  in  the  Rate  of  Growth 889 

Properties  of  New  Cells  and  Tissues 889 

Tensions  in  the  Cell-wall 390 

Tension  of  Tissues 890 

Geotropism 892 

Heliotropism 892 

Hydrotropism ,398 


CONTENTS.  XIX 

PAGE 

Thermotropism 394 

Assumption  of  Definite  Form  during  Growth 394 

Amount  of  Force  exerted  during  Growth 895 


CHAPTER  XHI. 
MOVEMENTS. 

Locomotion 397 

Movements  of  Chlorophyll  Granules  in  Leaves 398 

Hygroscopic  Movements 399 

Movements  due  to  Changes  in  Structure  during  Ripening  of  Fruits      .  400 

Revolving  Movements,  or  Circumnutation 400 

Methods  of  Observation 401 

In  Seedlings 403 

Of  the  Young  Parts  of  Mature  Plants     . 406 

In  Twining  Plant* 405 

Modified  Circumnutation 407 

rtvctitropic  or  Sleep  Movements 409 

Of  Cotyledons 411 

Of  Floral  Organs 412 

Times  of  Opening  and  Closing  of  Flowers 412 

Spontaneous  or  Autonomic  Movements 413 

Telegraph  Plant 413 

Cause  of  Autonomic  Movements  not  fully  known 414 

Sensitiveness 414 

Of  Roots 416 

Of  Stems  and  Branches *17 

Of  Tendrils 417 

OfPetioles 4 

Of  Leaf-blades *19 

Of  Sensitive  Plant *2° 

Of  Stamens ^ 

Effects  of  Anaesthetics  upon  Sensitiveness 424 


CHAPTER  XIV. 
REPRODUCTION. 

Individuality  in  Plants 426 

Methods  of  Reproduction 426 

FERTILIZATION  i»  ANGIOSFERMS 426 

The  Pistil 427 

The  Stigmatic  Secretion 427 

The  Pollen-grain 427 

Structure ** 

Content* 428 


xx  CONTENTS. 

PAGE 

Emission  of  the  Pollen-tube 

Time  required  for  the  Descent  of  the  Pollen-tube     .     .    .  «i 

The  Ovule 

Structure  and  Development 

Changes  following  Fertilization 

FERTILIZATION  IN  GYMNOSPERMS 

The  Pollen-grain 

The  Ovule 

Contact  of  the  Pollen  with  the  Ovule •    ;    •    * 

Contrast  between  the  Results  of  Sexual  and  Non-sexual  Reproduction     - 

Bud-propagation 4 

Apogamy 

Parthenogenesis 

Polyembryony ^ 

Close  and  Cross  Fertilization 447 

Nectar 461 

Secreting  glands 461 

Specific  Gravity 462 

Period  of  most  Copious  Secretion 452 

Colors  of  Flowers 462 

Odors  of  Flowers 464 

Hybridization 465 


CHAFfER  XV. 

THE  SEED  AND  ITS  GERMINATION. 

Nature  of  the  Life  of  the  Embryo 460 

Ripening  of  Fruits  and  Seeds 460 

Dissemination  of  Seeds 460 

Vitality  of  Seeds 461 

GERMINATION 462 

Conditions  of  Germination 462 

Moisture 462 

Access  of  Free  Oxygen 464 

Temperature 464 

Phenomena  of  Germination 466 

Fire-weeds .  469 


CHAPTER  XVI. 
RESISTANCE  OF  PLANTS  TO  UNTOWARD  INFLUENCES. 

Extremes  of  Heat  and  Cold 470 

Winterkilling .    ....  412 

Intense  Light 473 

Improper  Food 


CONTENTS.  XXi 

PAOB 

Poisons 473 

Noxious  Gases 473 

Liquids  and  Solids 476 

Mechanical  Injuries 476 


INDEX 


PHYSIOLOGICAL  BOTANY. 


INTRODUCTION. 


HISTOLOGICAL  APPLIANCES. 

THE  instruments  and  other  appliances  used  in  the  exami- 
nation of  minute  vegetable  structure  are,  with  the  exception  of 
a  few  special  ones  to  be  considered  later,  the  following :  — 

1.  Simple  microscope.      For  the  preliminary  preparation  of 
man}'  objects,  a  simple  stage-microscope  is  indispensable.     It 
should  be  furnished  with  only  the  best  lenses,  preferably  doub- 
lets or  triplets,  magnifying  from  ten  to  at  least  twenty  diameters. 
The  glass  portion  of  the  stage  should  be  not  less  than  an  inch 
and  a  half  in  diameter ;  supports  at  the  sides  of  the  stage,  on 
which  the  wrists  may  rest  during  dissections,  are  of  considerable 
use.     If  the  compound  microscope  described  below  is  provided 
also  with  an  inverting  eye-piece  and  with  an  objective  of  long 
focus,  it  can  be  made  to  serve  for  most  dissections  ;  otherwise  a 
simple  microscope  should  alwajTs  be  at  hand. 

2.  Compound  microscope.   When  reduced  to  its  simplest  terms, 
this  consists  of  a  stage,  or  flat  support  for  the  object  to  be  ex- 
amined, an  adjustable  tube  carrying  two  combinations  of  lenses, 
the  objective  and  the  eye-piece,  and  finally  some  means  of  illu- 
minating the  object.     The  desiderata  to  be  borne  in  mind  in  the 
selection  of  a  compound  microscope  for  use  in  Vegetable  His- 
tology, are  :  excellence  in  the  optical  parts,  ease  and  steadiness 
in  their  adjustment,  and  simplicity  of  construction.    Other  things 
being  equal,  a  microscope  with  a  short  tube  and  with  a  low 
stand  will  be  most  convenient,  on  account  of  the  large  number 
of  cases  in  which  reagents  must  be  employed,  their  application 
requiring  a  horizontal  stage. 


2  INTRODUCTION. 

3.  Three  objectiyes  and  two  eye-pieces,  from  combinations  of 
which  magnifying  powers  of  forty  to  eight  hundred  diameters 
can  be  obtained,  will  suffice  for  nearly  all  the  histological  work 
described  in  this  volume.     Two  objectives  and  a  single  eye- 
piece furnishing  powers  of  sixty  to  five  hundred  diameters  are 
enough  for  all  ordinary  investigations  of  minute  structure.    Ade- 
quate and  convenient  illumination  is  secured  by  a  plane  and  a 
concave  mirror  under  the  stage.     If  this  is  supplemented  by  an 
achromatic  condenser,  so  much  the  better.     The  stage,  prefer- 
ably thin,  should  be  provided  with  a  perforated  revolving  disc, 
or  other  suitable  system  of  diaphragms,  by  which  its  central 
aperture  can  be  made  larger  or  smaller. 

4.  The  student  ought,  at  the  outset  of  his  work,  to  make 
himself  familiar  with  the  principal  effects  which  are  produced 
in  the  appearance  of  the  object  in  the  field  of  the  microscope, 
by  changes  in  the  amount  and  direction  of  the  light  thrown  by 
the  mirror.     Details  can  sometimes  be  brought  out  clearly  by 
oblique  illumination,  which  are  only  faintly,  if  at  all,  seen  in 
direct  light. 

5.  In  general,  low  magnifying  powers  are  to  be  preferred  to 
higher  ones  ;  and  combinations  of  high  objectives  with  low  eye- 
pieces, securing  a  given  magnifying  power,  are  alwa}'s  better 
than  those  in  which  low  objectives  and  high  eye-pieces  are  used 
to  obtain  the  same  enlargement. 

6.  The  slips  of  glass,  or  "slides,"  upon  which  microscopic 
objects  are  commonly  prepared  and  preserved,  are  three  inches 
(76  mm.)  long  by  one  inch  (25  mm.)  wide.     This  is  for  most 
cases  a  more  convenient  size  than  that  frequently  emp^ed  in 
Germany ;  namely,  48  x  28  millimeters.     The  glass  should  be 
free  from  color  and  from  imperfections.     The  preparation  to  be 
examined  under  the  microscope  should  be  covered  with  a  disc 
of  thin  glass  before  it  is  brought  under  the  objective.     Perfect 
cleanliness  of  slide  and  cover-glass  is  absolutely  necessary  in  all 
examinations,  and  must  be  secured  by  the  exercise  of  scrupulous 
care.1 

7.  Dissecting  instruments.     Sharp  delicate  needles,  by  which 


For  cleaning  glass  perfectly,  the  following  preparation  may  be  used  :  — 
A  strong  solution  of  potassic  bichromate  to  which  about  half  as  much  con- 
centrated sulphuric  acid  is  cautiously  added.  To  this  mixture  add  an  equal 
volume  of  water.  The  glass  slips,  or  covers,  are  to  be  kept  in  this  solution  for 
a  short  time,  and  then  thoroughly  rinsed  in  pure  water,  after  which  they  may 
be  dried  with  cloth  or  wash-leather.  For  ordinary  use  alcohol  of  usual  strength 
answers  the  purpose  very  well. 


INTRODUCTION.  3 

the  parts  can  be  separated  by  teasing,  are  often  better  than 
any  cutting  instruments.  They  are  indispensable  in  the  ex- 
amination of  very  young  flower-buds,  and  of  great  use  in  the 
isolation  of  tissues  under  the  dissecting  microscope. 

8.  Sufficiently  thin  sections  of  soft  parts  may  be  made  by  any 
keen-edged  knife.     A  razor  of  good  quality  is  generally  to  be 
preferred  to  the  ordinary  dissecting  scalpel,  since  its  wide  and 
stiff  blade  can  be  held  with  greater  steadiness,  and  its  steel 
admits  of  as  sharp  an  edge.     As  a  rule,  the  razor  should  be 
dipped  in  water  before  using,  as  this  permits  the  steel  to  pass 
more  easily  through  tissues.1     If  the  parts  from  which  sections 
are  to  be  made  are  too  small  to  be  held  in  the  fingers,  they  can 
be  firmly  seized  between  slices  of  pith.     It  is  often  convenient 
to  imbed  the  object  in  paraffin  or  in  an  alcoholic  solution  of 
soap.2     These  melt  below  the  temperature  of  boiling  water,  but 
are  solid  at  ordinary  temperatures,  and  the  latter,  if  properly 
made,  is  transparent.      A  little  of  the  melted  imbedding  sub- 
stance is  poured  into  a  small  cone  of  glazed  paper,  and  when  it 
begins  to  cool,  the  object  is  placed  in  the  middle  of  the  mass. 
Upon  complete  cooling  it  is  firmly  held  therein. 

Before  putting  the  object  into  paraffin  it  should  first  be  satu- 
rated with  alcohol,  and  this  replaced  by  benzol  or  oil  of  cloves, 
in  order  to  enable  the  paraffin  to  hold  the  specimen  firmly.  The 
paraffin  may  be  dissolved  away  from  the  sections  b}f  application 
of  benzol,  oil  of  cloves,  or  turpentine  (see  also  110). 

9.  Thin   sections   are   best   removed    from    the  knife  by  a 
camel's-hair  pencil,  and  are  to  be  placed  at  once  in  water  or 
some  other  liquid.     Except  in  certain  cases,  water  ma}'  be  used 
as  a  medium  for  the  preliminary  examination  of  sections. 

10.  Microtome.     Any  of  the  simpler  microtomes,  or  section- 
cutters,  will  be  convenient  in  much  histological  work,  and  of 
great  use  in  the  preparation  of  a  series  of  sections  from  any 
very  minute  object,  since  this  permits  them  all  to  be  of  exactly 
the  same  thickness. 

11.  Measurements.      Microscopic    objects    are    measured    by 
micrometers.      The  eye-piece  micrometer  can  be  more  rapidly 
used  than  one  on  the  stage  of  the  instrument;  and  if  its  value 

1  Advantage  is  frequently  gained  by  moistening  the  edge  of  the  knife  with 
dilute  potassic  hydrate  before  dipping  it  in  water,  thus  removing  traces  of 
oil  which  may  have  adhered  to  it  during  sharpening.     But  potassic  hydrate 
should  not  be  used  in  this  way  if  reagents  are  to  be  subsequently  employed. 

2  Made  by  dissolving  enough  of  any  good  transparent  soap  in  hot  alcohol, 
to  form,  upon  cooling,  a  firm,  clear  mass. 


for  the  different  objectives  and  for  the  length  of  tube  has  been 
determined  accurately,  it  is  usually  preferable. 

The  values  of  the  spaces  in  the  eye-piece  micrometer  are 
ascertained  by  comparison  with  known  values  of  the  spaces  on 
a  standard  stage  micrometer ;  for  example,  if  one  space  in  the 
eye-piece  micrometer  corresponds  to  five  spaces  of  the  stage 
micrometer,  and  the  latter  has  a  value  of  one  thousandth  of  a 
millimeter,  each  space  of  the  former  equals  five  thousandths  of  a 
millimeter. 

The  unit  of  microscopic  measurement  is  the  "  micro-milli- 
meter," 1  one  thousandth  of  a  millimeter.  It  is  expressed  by 
the  Greek  //.. 

12.  Drawing.     An  image  of  the  object  under  the  microscope 
may  be  cast  by  reflection  upon  paper  at  the  side  of  the  micro- 
scope, by  means  of  a  Camera  lucida.      Several  forms  of  the 
Camera  lucida  are  adapted  to  use  with  the  tube  of  the  micro- 
scope in  a  vertical  position,  and  are  more  convenient  for  the 
majority  of  cases  coming  within  the  scope  of  the  present  work. 
Oberhauser's,  Milne  Edwards's,  and  Abbe's  are  of  this  kind. 

13.  Polarizing  apparatus.     This  is  of  great  use  in  the  exami- 
nation of  certain  contents  of  cells.      It  consists  of  two  Nicol 
prisms,  one  below  the  stage  of  the  microscope  and  receiving 
the  light  which  is  reflected  from  the  mirror,   the  other  in  the 
eye-piece.      Upon  turning  one  of  the  prisms,   distinctive  op- 
tical characters,  not  otherwise  seen,  are  presented  by  grains  of 
starch,  etc. 

14.  Media  and  reagents.      The  fluid  in  which  a  microscopic 
specimen  is  submitted  to  examination  is  technically  known  as  its 
medium.     Chemical  agents  subsequently  added  for  the  purpose 
of  producing  changes  by  which  the  chemical  character  of  the 
objects  may  be  recognized,  are  termed  reagents.     Some  of  the 
media,  however,  in  common  use  produce  characteristic  changes 
in  certain  cases,  and  might  be  as  truly  referred  to  the  latter 
class  as  several  of  the  reagents  themselves.    The  substances  in 


1  For  convenience  of  reference,  the  following  table  of  comparative  measure- 
ments is  given  :  — 

(u  INCHES.  INCHES.  M- 

6  000236 

7    000276 

8  000315 

9  000354 


10  000394 

One  meter  =  39.370432  inches. 


2.5399 
T^nr  =    25.3997 


253.9972 


INTRODtrCTIOtf.  5 

which  microscopic  specimens  are  preserved  are  termed  mounting- 
media. 

15.  MEDIA.      In  all  ordinar}*  cases  pure  water  is  the  best 
medium  in  which  to  place  the  object  for  examination.     If  dis- 
tilled water  cannot  be  procured,  filtered  rain-water  or  melted  ice 
will  answer  perfectly.      In  some  instances  water  produces  an 
immediate  change  either  in  the  cell-wall  or  in  the  contents  of 
the  cells.      For  instance,  the  superficial  cells  of  the  coats  of 
man}-  seeds  swell  up  at  once  when  they  are  placed  in  water,  and 
lose  their  former  shape  ;  on  the  other  hand,  important  contents 
in  the  seeds  of  man}-  plants  are  dissolved  immediately  when  the 
sections  are  moistened.     Hence,  other  media  must  be  sometimes 
substituted  for  water.     Absolute  alcohol  (see  40)   is  the  most 
useful  for  meeting  the  cases  above  referred  to.     Thus,  if  a  sec- 
tion of  a  seed-coat  be  first  examined  in  absolute  alcohol,  and  the 
alcohol  be  gradually  replaced  by  water  as  directed  in  17,  the 
changes  due  to  water  will  take  place  slowly,  and  can  be  watched 
throughout.     For  the  cases  in  which  the  cell  contents  are  sus- 
pected of  undergoing  change  from  water,  castor-oil  is  a  useful 
medium.      If  thought  best,  this  can  be  removed  subsequently 
from  the  specimen  by  alcohol  or  ether,  and  the  latter  in  turn 
ma}*  be  made  to  give  place  to  water,  and  the  changes  can  be 
followed  with  certainty. 

16.  Glycerin    (see    60),    either   concentrated   or   somewhat 
diluted  with  water,  is  a  bighty  useful  medium,  imparting  a  good 
degree  of  transparenc}-  to  most  specimens.     It  withdraws  a  part 
of  the  water  of  the  cell-sap,  and  in  the  case  of  thin-walled  cells 
this  is  followed  bj-  some  change  of  form.    The  remarkable  effects 
produced  upon  some  of  the  contents  of  cells  by  the  action  of 
glycerin  and  similar  agents  will  be  referred  to  under  Protoplasm. 

17.  One  medium  may  be  replaced  by  another  by  the  careful 
use  of  bibulous  paper.     Good  filtering  paper  is  the  best  for  this 
purpose.     If  a  little  of  the  liquid  which  it  is  desired  to  place 
under  the  cover-glass  be  put  at  the  edge  of  the  cover,  and  the 
opposite  edge  be  then  touched  lightly  with  the  paper,  the  liquid 
will  be  at  once  drawn  through.     B}-  successive  applications  of 
the  same  liquid,  the  specimen  can  be  thoroughly  washed  without 
removal  of  the  cover-glass. 

18.  REAGENTS.      Four  reagents  are  in  very  common  use  in 
nearly  all  histological  examinations ;  namel}*,  caustic  potash,  a 
solution  of  iodine,  an  acid,  and  a  staining  agent.     Even  in  ordi- 
nary cases,  however,  it  is  desirable  to  have  a  somewhat  wider 
choice  than  this,  and  therefore  the  following  brief  hints  are 


iNTBODtJOTlON. 

sa^srt;af»«S3t 

in  special  treatises  upon  ™ic^^®"^  ^t  5 

it,  .1  verv  small  amount  of  the 


action  ;  but  this  must  be  very  cautiously  done. 

20    If  one  reagent  is  to  be  followed  by  another,  attention 
must  be  given  to  the  effects  which  the  reagents  have  upon  each 
other,  or  upon  the  medium,  as  well  as  upon  the  specimen.     Fo* 
instance,  small  dark  crystals  of  iodine  separate  from  an  alcoholic 
solution  when  this  is  brought  into  contact  with  water.    1 
of  the  cover-glass  is  advised  in  all  cases  where  one  reagent  if 
be  washed  out  before  the  application  of  a  second,  or  where  < 
is  to  be  immediately  followed  by  another,  provided  the  specimen 
is  not  so  delicate  as  to  be  disturbed  by  it.     Some  parts  of 
specimen  are  apt  to  escape  action,  if  the  washing  or  the  intro 
duction  of  several  reagents  in  these  operations  is  comUicU 
without  lifting  the  cover;    but  by  the  exercise  of  great  car 
both  these  operations  may  be  carried  on  successfully  by  the  use 
of  bibulous  paper  without  removing  the  cover-glass. 

21.  Owing  to  their  importance,  potash   and  iodine  are  de- 
scribed first.     The   other  reagents   are   given   in   alphabetical 
order,  for  convenience  of  reference. 

22.  Potash,  Potassic  hydrate,  Caiistic  potassa,  are  names 
interchangeably  given  to  white  solid  potassa  and  to  its  solutions. 
This  substance  absorbs  carbonic  acid  so  eagerly  from  the  air, 
that  it  must  be  kept  in  glass-stoppered  bottles.     To  prevent  the 
stoppers  from  becoming  fastened  by  the  action  of  the  alkali  on 
the  glass,  it  is  well  to  smear  them  with  vaseline  or  paraffin. 

23.  Solutions  of  two  strengths  are  used.     I.   Concentrated. 
Solid  potassa  is  dissolved  in  the  smallest  amount  of  water  (not 
far  from  half  its  own  weight)  by  which  it  will  become  liquid. 
This  dense  syrupy  liquid  is  too  strong  for  ordinary  use.     II.   A 
common  solution  made  with  one  part  of  solid  potassa  in  three, 

1  Consult  the  following  :  Botanical  Micro-Chemistry,  by  Poulsen,  translated 
by  Trelease  (Cassino,   Boston),  1884.     Hilfsbuch  by  Behrens  (Schwetschke, 

Braunschweig),  1884. 


INTRODUCTION.  7 

five,  or  ten  parts  of  water,  depending  upon  the  particular  case 
in  which  it  is  to  be  used. 

•24.  For  use  as  a  macerating  agent  in  separating  cells,  a  strong 
.solution  is  preferable,  and  is  more  efficient  when  it  is  slightl}- 
warmed.  For  dissolving  or  rendering  transparent  most  of  the 
contents  of  cells,  more  dilute  solutions  are  better.  Owing  to  the 
prompt  effect  produced,  on  the  cell-wall,  and  upon  the  contents 
of  cells,  especially  of  young  ones,  a  moderately  strong  solution 
of  potassa  is  the  most  useful  clearing  agent  that  we  have.  After 
a  mass  of  tissue,  for  instance  an  embryo,  has  been  acted  on  by 
a  solution  of  potassa  until  it  has  become  translucent,  it  is  to  be 
cautiously  subjected  to  the  action  of  an  acid,  preferably  acetic 
or  hydrochloric,  and  then  washed.  A  second  treatment,  or  even 
a  third,  may  be  necessary  to  make  the  object  sufficiently  clear. 
Sometimes,  however,  the  potassa  renders  the  tissues  too  nearly 
transparent,  in  which  case  they  may  be  slightly  clouded  by  a 
little  alum-water.  This  process  of  clearing  tissues  was  first 
used  by  Hanstein  in  the  examination  of  the  tissues  at  points  of 
growth,  and  it  is  of  very  wide  applicability. 

25.  Some   structures   are   darkened    at   first   by   the   use  of 
potassa,  but  cautious  treatment  afterwards  with  a  dilute  acid 
and  a  second  application  of  potassa  will  generally  produce  a 
good  degree  of  transparency. 

26.  Potassa  is  a  solvent  for  many  of  the  substances  which 
incrust  the  cell-wall,  but  in  most  cases  the  solutions  must  be 
used  warm  ;   in  a  few  instances  heated  even  to  boiling.      The 
cell-wall,  washed  alter  such  treatment,  will  give  the  cellulose 
reactions  (see   145).      Suberin  can  thus  be  removed   from  the 
cell-walls  of  cork,  forming  with  the  potassa  yellowish  drops. 

27.  As  the  aqueous  solution  of  potassa  causes  considerable 
swelling  of  the  cell-wall,  it  is  desirable  to  have  also  at  hand 
an  alcoholic  solution.      This  is  best  made  by  mixing  95  per 
cent  alcohol  with  a  strong  aqueous  solution  of  potassa  until  a 
cloudiness  appears.      The   mixture  is  then  to  be  shaken   fre- 
quently, and,  after  a  day  or  so,  the  clear  liquid  above  is  to  be 
carefully  poured  off.     This  solution  may  be  diluted  with  alcohol 
if  necessary.1 

28.  Solutions  of  caustic  soda  can  replace  potassa  in  most 
of  the  foregoing  reactions.      The  special  cases  in  which  these 
alkalies  are  employed  for  the  identification  of  certain  contents 
of  cells  will  be  described  later. 

1  Russow's  Potash-alcohol. 


INTRODUCTION. 


menc  d'that  in  such  cases  a  minute  fragment  of  solid  iodine  be 
placed  in  lL  water  under  the  cover-glass  at  the  moment  of 


all  ordinary  examinations,  a  solution  of  iodine  in 
water  which  contains  iodide  of  potassium  is  used.     The  pro 
tions  employed  vary  widely.     A  convenient  strength  is  obtained 
by  dissolving  one'gram  of  iodine  and  five  grams  of  potass. 
iodide  in  enough  water  to  make  one  hundred  cubic  centimeters. 
Even  this  solution  is  too  strong  for  some  purposes.     In  a  few 
cases  a  different  solution  is  advised,  made  by  dissolving  five 
centio-rams  of  iodine  and  twenty  centigrams  of  potassic  mdirt 
fifteen  grams  of  water.1     But,  in  general,  dilute  solutions  are 
preferable. 

31  A  solution  of  iodine  and  iodide  of  potassium  in  glyce- 
rin is  employed  by  some.  An  alcoholic  solution  is  soineti 

82.  Iodine  is  a  characteristic  test  for  starch,  to  which  it 
imparts  a  blue  color,  depending  for  its  depth  chiefly  upon  the 
strength  of  the  solution.  Iodine  in  absolute  alcohol  gives  Witt 
dry  starch  a  brownish  color  ;  if  the  alcohol  is  not  absolute,  that 
is,  anhydrous,  a  blue  color  is  given  as  with  ordinary  aqueous 
solutions. 

33.  In  most  cases  cellulose  is  colored  pale  yellow  to  deep 
brown  by  iodine.  If  the  specimen  is  acted  on  by  concentrated 
sulphuric  acid,  either  just  before  or  just  after  the  application 
of  the  iodine,  a  blue  color  appears.  This  reaction  for  cellulose 
is  disguised  by  various  incrusting  matters,  which  can  be  removed 
by  strong  acids  or  alkalies;  after  their  removal  the  washed 
specimen  will  give  the  characteristic  cellulose  reaction  (see  also 
143). 

34.  Iodine  and  a  metallic  iodide  in  a  strong  solution  of  chlo- 
ride of  zinc  form  a  very  useful  reagent  for  cellulose,  to  which  a 
blue  color  is  given.  The  reagent  is  easily  made  by  dissolving 
pure  zinc  in  concentrated  hydrochloric  acid  until  there  is  no 
further  action  of  the  acid.  The  solution,  with  a  little  metallic 


1  Poulsen. 


INTRODUCTION.  9 

zinc  still  undissolved,  is  to  be  evaporated  to  a  syrupy  consist- 
ence, saturated  with  potassic  iodide,  and  lastly  enough  pure 
iodine  added  to  render  the  whole  a  deep  red  or  brown.  Cell- 
walls  that  have  incrusting  matters,  for  instance,  cork-cells  and 
most  wood-cells,  arc  turned  yellow  by  this  reagent.  It  is  known 
as  Schulze's  reagent.  Behreus  advises  the  preparation  of  modi- 
fications of  this  important  reagent,  all  depending  on  the  relative 
amount  of  iodine  and  the  degree  of  dilution.  A  little  practice 
in  their  use  will  suggest  the  cases  to  which  each  is  specially 
applicable.  Solutions  of  iodine  color  protoplasm,  and  other 
albuminoid  bodies,  yellow  to  deep  brown. 

35.  Owing  to  the  tendency  of  iodine  solutions  to  form  hydri- 
odic  acid,  it  is  recommended  by  many  authors  that  they  be  kept 
out  of  the  light ;  but  this  precaution  is  not  necessary  unless  the 
investigation  calls  for  pure  iodine  alone ;    in  such  a  case  it  is 
better  to  use  only  freshh-  prepared  solutions. 

The  following  reagents  are  arranged  in  alphabetical  order. 

36.  Acetic  acid.     Glacial  acetic  acid  diluted  by  two  or  four 
parts  of  water,  or  the  ordinary  concentrated  acid  of  the  shops,  is 
used  (1)  to  neutralize  the  alkali  in  Hanstein's  method  (see  24)  ; 
(2)  to  discriminate  between  oxalates  and  carbonates,  the  latter 
dissolving  with  effervescence  in   it,   the  former  remaining  un- 
changed in  it,  but  dissolving  quietly  in  hydrochloric  acid  ;  (3)  in 
the  study  of  the  nucleus. 

87.  Alcohol.  Common  strong  alcohol,  or  the  so-called  "95 
per  cent,"  is  widely  employed  for  the  preservation  of  micro- 
scopic material.  In  it  soft  tissues  become  hardened.  This  is  a 
great  advantage  in  the  case  of  specimens  which  are  too  yielding 
to  be  cleanly  cut  when  fresh.  If  it  is  desirable  to  again  soften 
tissues  which  have  been  hardened  by  the  action  of  alcohol,  it  is 
merely  necessary  to  soak  them  for  a  short  time  in  water,  when 
they  will  assume  nearly  the  consistence  they  had  when  fresh. 
This  reagent  produces  certain  marked  changes  in  the  contents  of 
vegetable  cells :  the  protoplasmic  matters  become  more  or  less 
shrunken,  many  oils  and  fats  are  dissolved,  and  certain  sub- 
stances in  solution  in  the  cell-sap  are  separated  out  (see  183). 

38.  The  air  which  ocelli's  in  intercellular  spaces  and  in  all 
dry  specimens  is  generally  removed  with  ease  by  the  action  of 
alcohol,  especially  if  a  little  heat  is  applied. 

39.  Alcohol  is  of  use  also  in  the  preparation  of  some  of  the 
staining  agents. 

40.  Absolute  alcohol  contains  only  the  merest  trace  of  water. 
Hence  it  must  be  used  instead  of  ordiuarv  alcohol  whenever  the 


INTRODUCTION 

- 


be  used  to 


Aqueous  ammonia  may  rep1.ee  the  fixed 
alkalies    potassa  and  soda,  but  possesses  no  advantage  over 
£  eicept  in  its  somewhat  slower  and  less  violent  actio^ 
For  its  use  in  the  examination  of  albuminoids,  see  126. 
principal  use  in  microscopy  is  in   the   preparation   ot  certi 
stainino-  agents  (see  77)  and  cuprammoma. 

43  Anilin  chloride.  Dissolved  in  alcohol,  this  reagent  im- 
parts a  pale  yellow  color  to  lignified  cell-walls.  Upon  addition 
of  hydrochloric  acid,  the  color  is  much  deepened.  This  is  Hohnel  i 
test  for  lignin. 

44.  Anilin  sulphate.     This  substance  in  aqueous  or  alcohol 
solution  gives  to  lignified  cell-walls  a  pale  yellow  color,  which  is 
much  deeper  when  the  reagent  is  followed  by  sulphuric  acid,  — 
Wiesner's  test  for  lignin. 

45.  Argentic  nitrate,  or  nitrate  of  silver,  in  extremely  di 
alkaline  solution  freshly  made,  has  been  recommended  for  dis- 
criminating between  living  and  dead  protoplasm,   the  former 
turning  dark,  the  latter  remaining   unchanged  (see  details  in 
Part  II.). 

46.  Asparagin.     A  concentrated   solution   of  asparagin   is 
suggested  by  Borodin  for  the  recognition  of  asparagin   itself 
when  its  crystals  have  been  formed  in  tissues  blanched  by  dark- 
ness. 

47.  Auric  chloride,  long  used  for  staining  preparations  in 
animal  histology,  has  been  somewhat  employed  for  coloring  the 
cells  of  certain  lower  plants,  and  in  the  same  manner  as  argentic 
nitrate,  for  detecting  the  condition  of  protoplasm. 

48.  Benzol  is  a  powerful  solvent  for  various  vegetable  fats 
and  resins.     It  is  also  used  for  the  preparation  of  benzol-balsam 
(see  112),  and  in  dissolving  paraffin  (see  8). 

49.  Calcic  chloride.     Treub   employs  this  for   clearing  tis- 
sues.     The  fresh  section,  after  having  been  moistened  by  a 
little  water,  is  covered  with   dry  powdered   chloride,  warmed 
until  it  is  about  dry,  and  afterwards  placed  in  a  little  water. 


INTRODUCTION.  11 

From  this  it  is  to  be  transferred  to  glycerin,  where  it  soon 
becomes  clear.1 

50.  Calcic  hypochlorite  in  aqueous  solution  bleaches  many 
tissues  without  the  use  of  an  acid,  but,  in  general,  specimens 
which  have  been  subjected  to  its  action  are  more  thoroughly  de- 
colorized if  they  are  subsequently  placed  in  dilute  hydrochloric 
acid,  washed  in  pure  water,  and  finally  transferred  to  glycerin. 
Preparations  which  have  been  bleached  by  this  method  are  easily 
colored  by  some  of  the  staining  agents  described  on  page  15. 
Sodic  hypochlorite  may  replace  it  in  all  cases. 

51.  Carbon  disidphide  is  used  as  a  solvent  for  fats. 

52.  Carbolic  acid,  or  phenol,  dissolved  in  the  least  quantity 
of  concentrated  hydrochloric  acid  which  will  lake  it  up,  gives 
a  green  color  with  lignified  cells.     It  is  better  to  add  to  a  few 
drops  of  the  strongest  hydrochloric  acid  a  small  quantity  of 
crystallized  phenol,   warm   the  mixture   slightly,  and  upon  its 
cooling  add  enough  acid  to  remove  any  cloudiness. 

53.  Chloral  hydrate  in  aqueous  solution  is  recommended  by 
Arthur  Meyer a  as  a  clearing  agent.      Two  parts  of  water  are 
added  to  five  parts  of  chloral,  and  used  somewhat  above  the 
temperature  of  15°  C. 

54.  Chromic  acid.     The  pure  acid,  in  strong  solution,  acts 
promptly  on  cell-walls,  dissolving   all   except  those  which  are 
silicificd  and  those  which  are  cutinized.      Even  the  latter  yield 
to  prolonged  action.     If  the  solution  is  more  dilute,  the  action 
goes  on  only  so  far  as  to  cause  swelling  of  the  cell-wall,  bring- 
ing out,  in  special  cases,  a  veiy  distinct  stratification.     .Solutions 
which  are  so  dilute  as  to  be  merely  pale  yellow  cause  hardening 
of  soft  tissues,  and  this  acid  therefore  forms  an  excellent  adju- 
vant to  alcohol  for  this  purpose  (see  Part  II.). 

55.  Ctiprammonia.      To  a  solution  of  cupric  sulphate  add 
enough   soda    (or   potassa)    to   produce   a   precipitate.      After 
removal  of  the  excess  of  liquid  by  filtration,  place  the  precipitate 
in  a  flask,  wash  once  with  water  which  has  been  freed  from  air  by 
boiling,  and  then  dissolve  the  mass  in  the  least  quantity  of  con- 
centrated ammonia  which  will  take  it  up.      The  freshly  prepared 
solution    should    act   promptly  on .  delicate  fibres  of  cellulose, 
cotton  for  example,  causing  them  to  swell  and  apparent!}'  pass 
into  solution.      Lignified  and  cutinized  cell-walls  are  not  acted 


1  Flahault:  Aecroissement  terminal  de  la  raciiie.     Ann.  lies  Sc.  uat.,  1878. 
vi.    p.  24. 

2  Das  Chlorophyllkoru,  Leipzig,  1883. 


12  INTRODUCTION. 

upon  until  the  foreign  matter  has  been  removed  by  the  agents 
previously  spoken  of  (see  26). 

This  reagent,  known  as  Schweizer's,1  possesses  its  chief  in- 
terest from  the  fact  that  it  is  the  only  liquid  known  in  which 
cellulose  appears  to  dissolve  without  essential  change  of  compo- 
sition. It  has  a  limited  application  in  the  discrimination  of 
fibres  used  in  the  arts. 

56.  Cupric  acetate  in  aqueous  solution  is  used  as  a  preparatory 
liquid  for  the  examination  of  resins.     The  part  to  be  examined 
is  kept  in  a  concentrated  solution  for  some  days,  and  sections 
are  then  made  from  it.     If  certain  resins  are  present,  they  will 
appear  of  a  green  color.    The  above  is  Franchiniont's  test  based 
on  a  reaction  discovered  by  Unverdorben.2 

57.  Cupric  sulphate  in  saturated  aqueous  solution  is  used 
for  the  detection  of  certain  carbohydrates  (see  184)  and  albnmi- 
noidal  matters  (see  124).    Commercial  blue  vitriol,  recrystallized 
two  or  three  times,  will  answer  for  all  ordinary  cases. 

58.  Ether  is  used  as  a  solvent  for  fats,  etc. 

59.  Ferric  chloride  in  aqueous  solution  was  formerly  recom- 
mended as  a  test  for  the  tannins;8  the  tannin  of  oak-bark  be- 
coming bluish-black  ;  that  in  the  leaves  of  the  sumach,  greenish- 
black.     But  the  distinctions  are  not  constant.     Ferric  acetate 
and  sulphate  are  now  more  generally  used  than  the  chloride  as 
a  test,  and  are  better. 

60.  Glycerin.     Only  the  purest  glycerin  should  ever  be  em- 
ployed in  microscopic  examinations.     The  following  are  among 
the  most  important  of  its  many  applications:    1.   In  clearing 
specimens.     It  is  used  not  only  as  an  adjuvant  in  the  Hanstein 
and  other  methods  of  clearing,  but,  in  man}*  cases,  it  serves  well 
without  any  other  reagent.     2.  To  cause  withdrawal  of  water 
from  fresh  cells,  the  degree  of  effect  depending  on  the  strength 
of  the  glycerin.      3.  In  the   examination  of  protein   granules 
(see  175).     4.    As  a  test  for  inulin ;    this  substance  separates 
sooner  or  later  in  the  form  of  sphserocrystals.     5.  As  a  solvent 
for  iodine  (see  31). 

61.  Hydrochloric  acid.    Pure  concentrated  acid  is  one  of  the 
most  satisfactory  agents  for  the  maceration  of  woody  tissues. 
When  dilute,  it  serves  for  the  discrimination  between  carbonates 
and  oxalates,  the  former  dissolving  with  effervescence,  the  latter 


-  Schweizer:  Vierteljahrsschrift  natur.  Ges.,  Zurich,  1857. 

2  Behrens:Hilfsbuch,  ]..  377. 

8  Watts's  edition  of  Fownes's  Chem.,  p.  672. 


INTRODUCTION.  13 

without.      It  must    be  remembered   that  acetic  acid  dissolves 
carbonates,  but  not  oxalates  (see  36). 

This  acid  has  been  used  by  Pringsheim l  in  the  study  of 
chlorophyll  grains ;  fresh  sections  of  tissues  containing  chloro- 
phyll being  exposed  to  the  action  of  the  acid  for  some  hours. 
From  the  grains,  minute  spheres  of  a  brownish  color  become 
nearly  detached,  and  these  afterwards  appear  as  clusters  of 
acicular  crystals  (see  Part  II.).  Hydrochloric  acid  is  also  of 
use  in  the  examination  of  some  protein  matters  (see  124). 

62.  Indol  (Niggl's  test2  for  lignin)  is  used  in  an  aqueous  so- 
lution.   The  specimen,  subjected  to  the  action  of  the  solution  for 
a  few  minutes,  is  transferred  to  sulphuric  acid  of  specific  gravity 
1.2  (made  by  adding  one  part  of  concentrated  acid  to  four  parts 
of  water).     Lignified  structures  become  red. 

63.  Mercuric  c/iloride,  or  corrosive  sublimate,  dissolved  in 
fifty  parts  of  absolute  alcohol  renders  protein  grains  insoluble 
in  water.    Pfeffer8  recommends  that  the  specimen  should  remain 
in  this  reagent  at  least  twelve  hours.      Dippel4  uses  a  dilute 
aqueous  solution  (1  in  500)  to  render  visible  the  currents  in  the 
most  delicate  threads  of  protoplasm  (and  for  the  demonstration 
of  the  nucleus  without  affecting  the  other  contents  of  the  cell). 

64.  MHlorfs  reagent,  common!}'  called  acid  nitrate  of  mercury, 
is  best  prepared,  according  to  its  discoverer,  by  pouring  upon 
pure  mercury  its  own  weight  of  concentrated  nitric  acid.     For 
a  short  time  the  action  is  violent ;  when   it   subsides  a  little, 
gently  warm  the  liquid  until  the  metal  is  completely  dissolved. 
The  solution  is  Immediately  diluted  by  twice  its  volume  of  pure 
water.     After  a  few  hours  the  liquid  is  to  be  decanted  from  the 
crystalline  mass  which  has  formed, 'and  it  is  then  ready  for  use.6 

This  reagent  is  more  efficient  when  freshly  made. 

Albuminoid  substances  are  colored  jred  by  this  reagent  even 
in  the  cold,  but  much  more  readily  upoii  the  application  of  heat. 
According  to  Millon,  the  reaction  is  due  to  the  presence  in  the 
liquid  of  both  mercuric  nitrate  and  nitrite. 

This  reagent  has  been  employed  for  the  demonstration  of  the 
stratification  and  spiral  striation  of  certain  cell-walls. 

65.  Nitric  acid  gives   to   protein   matters  a   yellow   color, 
which  is  intensified  upon  the  subsequent  use  of  ammonia.     The 


1  Pringsheim's  Jahrbiicher,  Bd.  xii.  p.  294,  et  seq. 

2  Flora,  1881,  p.  545,  et  seq. 

8  Pringslieiiu's  Jahrbiicher,  viii.  p.  441. 
*  Dippel:  Das  Mikroskop,  i.  p.  281. 
5  Quoted  from  Behrens:  Hilts!.,  p.  247. 


14  INTRODUCTION. 

same  treatment,  especially  if  the  slide  is  slightly  warmed,  colors 
the  so-called  intercellular  substance  yellow.  The  acid  is  also 
used  as  a  test  for  suberin  (see  158). 

66.  Ostnic  acid  (perosmic  acid)  is  very  volatile,  and  there- 
fore is  best  preserved  in  sealed  glass  tubes  until  wanted  for  use, 
when  the  tube  can  be  broken  under  water.    Even  from  the  aque- 
ous solution  the  irritating  acid  escapes  in  small  amount,  render- 
ing it  a  disagreeable  reagent  to  work  with.     The  solutions  are 
usually  of  one  per  cent  strength. 

Oils  are  colored  brown  by  the  reduction  of  the  acid  to  me- 
tallic osmium  on  the  surface  of  the  drops.  Living  protoplasm 
is  killed  at  once  by  even  dilute  solutions  of  this  acid,  and  there 
is  usually  more  or  less  discoloration  of  the  different  parts. 
Hence  it  is  a  useful  agent  for  arresting  the  processes  of  cell- 
division  and  growth  at  any  desired  stage.  Advantage  is  some- 
times gained,  according  to  Poulsen,1  by  the  combination  with  it 
of  chromic  acid. 

67.  Phenol  (see  carbolic  acid,  52). 

68.  Phloroglucin,  used   by  Wiesner  as  a  test  for   lignin.1 
The  specimen  is  first  acted  on  by  hydrochloric  acid,  and  then 
moistened  by  a  solution  of  phloroglucin  in  water  or  alcohol.     If 
the  cell-walls  are  lignified,  they  will  at  once  assume  a  red  color. 
Hohnel8  suggests  the  employment  of  a  strong  decoction  of  cherry- 
wood  instead  of  the  phloroglucin.     Used  in  the  same  way,  it  im- 
parts a  violet  color  to  lignified  cells.      This  test  is  hardly  so 
satisfactory  as  the  other. 

69.  Potassic  bichromate  in  aqueous  solution  is  used  to  harden 
tissues,  and  is  about  as  good  as  chromic  acid.     It  has  been  also 
employed  by  Sanio4  for  the  detection  of  tannin. 

70.  Potassic  chlorate,  used  with  nitric  acid,  is  the  most  con- 
venient macerating  agent.     If  a  few  small  crystals  of  this  salt 
are  added  to  a  little  concentrated  nitric  acid  in  a  test-tube  con- 
taining a  fragment  of  wood,  and  the  liquid  is  carefully  warmed, 
violent  action  begins  somewhat  below  the  point  of  boiling,  and 
the  wood  is  speedily  disintegrated.      By  selecting  acid  of  the 
right  strength,  and  by  careful  regulation  of  the  heat  applied,  the 
action  of  the  liquid  can  be  kept  well  under  control,  so  that 
almost  any  degree  of  action  can  be  obtained.     It  is  not  safe  to 
use  this  reagent  in  the  room  where  delicate  apparatus  is  kept, 

1  Mikrochemie,  p.  19. 

2  Sitzungsber.  Akad.  Wieii,  1878,  p.  60. 
8  Ib.  1877,  p.  685. 

4  Bot.  Zeitung,  1863,  p.  17. 


INTRODUCTION.  15 

since  the  gases  evolved  act  upon  metals.      This  is  Schulze's 
macerating  process. 

71.  Potassic   nitrate,1    used  in   the   examination   of  proto- 
plasm (see  Part  II.). 

72.  Rosolic  acid,  or  corallin,  dissolved  in  water  containing  a 
trace  of  sodic  carbonate,  forms  a  purple  fluid  which  colors  vege- 
table mucus  red.     It  is  used  also  to  demonstrate  the  structure  of 
cribrose-tissue.2 

73.  Schweizr.r*tf  reagent  (see  cuprammonia). 

74.  Sodic  cfdoride  (common  salt),  used  in  aqueous  solution 
in  the  examination  of  protoplasm  (see  120). 

75.  Sugar.     Cane  sugar  dissolved  in  water  to  form  a  thick 
syrup  is  allowed  to  act  for  some  time  on  tissues  containing  pro- 
toplasm :  a  drop  of  concentrated  sulphuric  acid  is  then  placed 
on  the  object,  when  the  protoplasm  will  take  on  a  faint  rose-red 
color.     The  reaction  is  uncertain. 

76.  Sulphuric  acid.     Pure  concentrated  acid  is  used  as  an 
adjuvant  in  many  tests,  e.g.,  with  iodine  solutions  in  the  identi- 
fication of  cellulose,  but  it  is  also  of  great  use  by  itself  in  break- 
ing down  cellulose.      By  it,  a  cellulose  wall  can  be  destroyed 
without  destruction  of  the  protoplasm  within  (see  141). 

77.  Staining  agents.     A  few  of  the  chemicals  in  the  foregoing 
list  impart  to  certain  tissues,  and  certain  contents  of  cells,  colors 
which  have  a  good  degree  of  permanence  when  the  specimens 
are  preserved  in  a  suitable  medium.     But  the  colors  produced 
by  most  reagents  are  fugitive,  and  serve  only  a  temporary  pur- 
pose.    When,  therefore,  it  is  desirable  to  stain  or  tinge  a  given 
part  of  a  specimen  permanently,  recourse  must  be  had  to  dyes 
which  do  not  readily  fade. 

78.  Some  of  these  have  been  long  in  use  in  Vegetable  His- 
tology for  the  purpose  of  preparing  attractive  specimens  for  the 
demonstration  of  tissues,  but  it  is  only  within  a  recent  period  that 
the}*  have  been  successfully  employed  in  the  stud}"  of  cell-divi- 
sion.    In  the  examination  of  the  changes  which  take  place  in 
the  interior  of  cells  during  division,  they  are  indispensable :  in 
the  examination  of  the  tissues  themselves,  their  use  is  fur  from 
satisfactory.      As  will  be  specially  shown  later,  the  chemical 
differences  between  the  cell-walls  of  certain  tissues  which  it  is 
desirable  to  distinguish  from  each  other  under  the  microscope 
are  not  very  great,   and  they  often  behave  alike  as  respects 

1  Treub:  Naturk.  Verh.  d.  koningl.  Akad.  vol.  xix.,  1878,  p.  9. 

2  Behrens:  Hilfsbuch,  p.  313. 


INTRODUCTION. 


ta       Hpnce  it  is  impossible  to  lay  down  rules 

to  S  eaL  in  whic'h  tissues  are  to  be  stained  : 

The  staging  of  the  nucleus,  however,  can  be  readily  secured  by 

fl™e  explicit  directions  given  in  the  chapter  on  "  Cell- 

^  79tUOf  the  whole  class  of  staining  agents,  it  may  be  said  that 
exposure  to  strong  light  diminishes  the  brilliancy  of  the  coloring 
they  Foduce  in  the  specimen,  and  in  many  cases  complete  y 
destroys  it  In  general,  the  staining  obtained  by  allowing  the 

£*£.  *  «S  for  a  long  time  in  a  <lilu?  solution, 

dye  is  more  satisfactory  than  when  a  stronger  dye  is  use< 


e>  CARMIN.  Two  grades  are  readily  procurable  in  this  coun- 
try ;  'namely,  (1)  "  No.  40,"  (2)  »  Orient."  The  former  is  the 
cheaper  and  will  answer  for  all  cases  described  in  this  treatise  ; 
but  attention  must  be  called  to  the  fact  that  it  is  sometimes 
adulterated,  and  hence  it  may  be  found  necessary  to  change  the 
proportions  given  in  the  following  formulas.  A  good  carmm, 
even  of  the  grade  first  mentioned,  should  leave  only  little  residue 
when  placed  in  strong  ammonia.  If  more  than  a  trace  of  resi- 
due is  found,  the  amount  of  carniin  in  the  formula  must 
proportionately  increased. 

81.  Ammonia-carmin.  Pure  powdered  carmin  is  rubbed 
up  with  a  little  water  to  form  a  thin  paste,  enough  strong  am- 
monia to  dissolve  it  is  cautiously  added,  and  the  whole  is  then 
filtered.  The  filtrate  is  to  be  evaporated  slowly  over  a  water- 
bath.  The  dried  mass  dissolves  readily  in  water,  forming  a 
clear  liquid  which  keeps  well  ;  but  it  is  better  to  preserve  the 
mass  in  a  tightly-stoppered  bottle,  dissolving  it  only  as  required 
(Hartig's  carmin).1 

82.  A  modification  of  this  carmin  is  made  as  follows:  .2  to 
.4  gram  of  carmin  is  shaken  up  with  80  c.  c.  of  water,  and  a 
few  drops  of  ammonia  added.  A  part  of  the  carmin  dissolves, 
and  is  to  be  filtered.  If  the  filtrate  smells  strongly  of  ammo- 
nia, it  is  allowed  to  stand  for  half  a  day  under  a  bell-jar.  A 
drop  of  ammonia  will  re-dissolve  any  slight  trace  of  carmin 
which  may  separate.  This  fluid  is  to  be  added  to  water,  drop 
by  drop,  until  the  right  color  is  obtained  (Gerlach's  ammonia- 
carmin).2 

83.   If,  to  the  filtrate  last  mentioned,  30  grams  of  glycerin 

1  Uippel  :  Das  Mikroskop,  i.  p.  284. 

2  Behrens-.Hilfsbuch,  p.  257. 


INTRODUCTION.  17 

and  10  grams  of  strong  alcohol  are  added,  a  liquid  is  obtained 
which  is  known  as  Frey's  glycerin-carmin. 

84.  Bealds  carmin  is  nearly  the  same.    Ten  grains  of  carmin 
are  placed  in  a  test-tube,  and  half  a  drachm  of  strong  ammonia 
added ;  the  mixture  is  shaken,  and  gently  heated  over  a  spirit- 
lamp.     The  solution  is  to  be  boiled  for  a  few  seconds  and  then 
allowed  to  cool.     In  an  hour  two  ounces  of  gtycerin  and  two 
ounces  of  water  are  to  be  added,  together  with  half  an  ounce  of 
alcohol ;  the  liquid  is  then  filtered.1  « 

85.  TlnerscfCs  borax-cartnin.3     2  grams  of  borax  are  dis- 
solved in  28  c.  c.  of  distilled  water,  and   .5  gram  of  carmin 
added.     The  solution  is  next  mixed  with  60  c.  c.  of  absolute 
alcohol,  and  filtered. 

86.  Thiersclis  oxalic-acid  carmin.*     1   gram  of  carmin  is 
dissolved  in  1  c.  c.  of  ammonia  and  3  c.c.  of  water.     Another 
solution  is  prepared  by  dissolving  8  grams  of  crystallized  oxalic 
acid  in  175  c.c.  of  water.     The  two  solutions  are  then  mixed, 
16  c.c.  of  absolute  alcohol  added,  and  the  whole  filtered.     This 
liquid  is  violet  when  ammonia  is  in  excess  ;  orange,  if  too  much 
oxalic  acid  is  present. 

87.  Grenadier's  alum-cannin.*     Carmin  is  dissolved  in  a 
solution   of  potash-alum   or  ammonia-alum  until   the  required 
color  is  obtained.     This  has  been  modified  by  Tangl  as  follows : 
To  a  saturated  solution  of  alum,  enough  carmin  is  added  to  give 
a  deep  color  (1  grm.  in  100  c.c.  of  solution),  the  whole  boiled 
for  ten  minutes,  and  filtered  upon  cooling. 

88.  Woodward's  carmin.      kt  Pulverized  carmin  7|  grains, 
water  of  ammonia  20  drops,  absolute  alcohol  half  an  ounce, 
glycerin  1  ounce,  distilled  water  1  ounce.     Put  the  pulverized 
carmin  in  a  test-tube  and  add  the  ammonia.     Boil  slowly  for  a 
few  seconds,  and  set  aside  uncorked  for  a  day,  to  get  rid  of  the 
excess  of  ammonia.     Add  the  mixed  water  and  glycerin,  and 
next  the  alcohol,  and  filter." 

89.  Carmin  with  picric  acid.     This  agent,  known  as  Ran- 
vier's  picrocarmin,  is  made  by  cautiously  adding  to  a  concentrated 
solution  of  picric  acid  enough  ammonia-carmin  solution   (81) 
to  saturate  it,  and  then  evaporating  to  one-fifth  the  volume. 

1  Beale :  How  to  Work  with  the  Microscope,  p.  125. 
«  Behrens:  Hilfsbuch,  p.  258. 

3  Behrens:  Hilfsbuch,  p.  257.     In  Dippel(Das  Mikroskop),  p.  285,  the  pro- 
portions are  somewhat  different. 

4  Archiv.  fur  Mikrosk.  Anat.,  1879,  p.  465.     Tangl,  in  Pringsh.  Jahrb., 
Bd.  xii.,  1880,  p.  170. 

2 


18  INTRODUCTION. 

Upon  cooling,  a  slight  sediment  is  deposited.  After  filtration 
from  this  sediment  the  liquid  is  evaporated  to  dry  ness,  and 
afterwards  dissolved  in  water  in  the  proportion  of  1  : 100. 

Another  formula  is:  1  gram  of  carmin  and  4  e.c.  of  concen- 
trated ammonia  are  mixed  with  200  c.c.  of  water,  and  5  grains 
of  picric  acid  then  added.  After  nearly  complete  solution  the 
clear  liquid  is  poured  off',  and  exposed  to  the  air  for  some  weeks. 
The  red  powder  left  after  this  slow  evaporation  is  to  be  dis- 
solved when  required  in  water  in  the  proportion  of  2  :100.  and 
the  solution  filtered  through  two  thicknesses  of  filter-paper. 

Cochineal,  the  substance  from  which  carmin  is  prepared,  may 
be  used  in  aqueous  extract,  or  with  alum.  The  formula  for  the 
preparation  with  alum  is  given  as  follows :  Rub  to  a  fine  powder 
one  gram  of  cochineal  with  one  gram  of  burnt  alum  ;  mix  with 
100  c.  c.  of  water,  and  boil  down  to  00  c.  c.  When  cold,  filter  the 
solution  several  times,  and  add  a  few  drops  of  carbolic  acid. 

90.  Hcematoxylin  (a  dye  obtained  from  logwood)  is  used  dis- 
solved in  alcohol,  or  alum-water,  according  to  circumstances. 

Frey  gives  the  formula  :  1  gram  of  hannatoxylin  is  dissolved 
in  absolute  alcohol.  This  solution  is  added,  drop  by  drop,  to  a 
three  per  cent  aqueous  solution  of  alum,  until  it  becomes  deep 
violet  in  color.  After  exposure  to  the  air  for  a  few  days,  it  is 
to  be  filtered,  and  is  then  ready  for  use ;  but  a  fresh  filtration 
will  be  found  necessary  after  a  time.  Poulsen  advises  that  a 
few  drops  of  a  ten  per  cent  solution  of  alum  be  added  to  an 
aqueous  solution  of  hiematoxylin  (.35  gram  in  10  c.c.  water). 

Aqueous  extracts  of  several  other  dye-woods  can  replace 
haematoxylin  in  some  cases,  but  they  have  no  advantage  over  it. 

91.  Picric  acid  (trinitrophenic  acid)  in  aqueous  solution  is 
valuable  for  staining  and  hardening  protoplasm.     It  may  be 
used  alone,  combined  with  carmin  (see  89),  or  with  nigrosin. 

92.  Alkanet-root  (alkanna)  in  alcoholic  solution  tinges  resin- 
ous globules  and  serves  to  prepare  for  cutting  specimens  which 
contain  them.    The  method  of  use  is  described  under  "  Resins." 

93.  The  coal-tar  colors.     Under  this  name  are  comprised  the 
anilin  derivatives  and  a  few  others  of  a  slightly  different  origin. 
The  following  table  will  indicate  to  some  extent  the  changes  of 
color  which  may  be  expected  when  these  dyes  are  used  with 
tissues  which  have  a  marked  acid  or  alkaline  reaction.     But  it 
should  be  observed  that  the  names  of  several  of  the  dyes  are 
loosely  applied,  and  that  the  dyes  made  by  different  manufac- 
turers are  not  always  of  the  same  character  or  strength.     All  of 
the  dyes  mentioned  below  are  soluble  in  water  and  alcohol. 


INTRODUCTION. 


19 


Name. 

Effect  of  dilute  HC1. 

Effect  of  dilute  Ammonia. 

Bed  dyes. 

Magenta. 

Color  fades  to  brown  or  light 
purple. 

Fades  completely. 

Safranin. 

Color  changes  to  purple,  nnd 

Little  change. 

a  brown  precipitate  occurs. 

Red  anilin. 
Acid  azo-rubin. 

Deep  orange-brown  color 
Slight  change  of  tint. 

Reddish  precipitate. 
Little  change. 

Eosin. 
Ponceau. 

Orange  precipitate. 
No  change  of  color 

No  marked  change. 
No  change. 

Yellow  and  Orange  dyes. 

Solid  yellow. 
Orange  "R." 
Gold  orange. 

Purple  precipitate. 
Unchanged. 
Little  change. 

Little  change. 
Unchanged. 
Color  deepens  to  red. 

Green  dyes. 

Methyl-green. 

The  bluish  tint  becomes  deep         Fades  out. 

Brilliant  green.            * 
Emerald  green. 

green. 
Fades  somewhat. 
Fades  out. 

Whitish  precipitate. 
Whitish  precipitate. 

Jiliie  and  V'wltt  dye*. 

Cotton-blue  "  B."                          Unchanged. 

Fades  somewhat. 

Methyl-Tiolet  '•  BBBBBB." 
Nigrosin. 

Greenish  precipitate. 
Little  change. 

Purple  precipitate. 
Little  change. 

94.  A  solution  of  any  of  the  above  dyes  consisting  of  one 
gram  with  enough  water  to  make  one  hundred  cubic  centimeters, 
although  too  strong  for  most  cases,  is  very  convenient,  since  it 
can  easily  be  diluted  at  will.     From  even  very  dilute  solutions 
parts  of  a  specimen,  for  instance,  a  cross-section  of  a  stem,  will 
take  up  some  of  the  color  with  more  or  less  change.      If  the 
staining  is  too  deep,  a  part  of  the  color  can  be  removed  by 
careful  washing  in  alcohol,  or  in  a  very  dilute  acid  or  alkali 
(see  aliove  table  for  each  case). 

95.  Double-staining.     It  is  sometimes  possible  to  color  dif- 
ferent parts  of  a  specimen  with  more  than  one  dye  ;  for  instance, 
staining  the  fibres  of  the  bark  green,  and  the  wood  of  the  same 
specimen  red.     The  best  results  are  obtained  by  the  use  of  an 
alcoholic  solution  of  one  of  the  dyes  and  an  aqueous  solution  of 
the  other.     The  following  method  proposed  by  Rothrock1  gives 
excellent  results.     The  dyes  are  Woodward's  carmin  (see  88) 
and  anilin  green  (or  '"  iodine  green").     The  specimen  (whether 
bleached   by    sodic    hypochlorite   or    left   unbleached)    is   first 
thoroughly  saturated  by  alcohol,  which  hardens  it,  and  causes 
contraction  of  the  contents  ;  it  is  then  kept  for  a  day  in  a  dilute 


1  Jiotanical  Gazette,  September,  X879. 


20  INTRODUCTION. 

alcoholic  solution  of  anilin  green.  In  a  row  of  watch-crystals 
the  following  liquids  are  placed:  (1)  water,  (2)  Woodward's 
carmin,  (3,  4,  5)  alcohol,  (6)  absolute  alcohol,  (7)  oil  of  cloves. 
The  specimen,  taken  from  the  green,  is  dipped  for  a  moment  in 
water,  then  for  about  a  minute  in  the  carmin,  then  successively 
through  the  alcohols,  in  each  of  which  it  remains  ten  to  twenty 
minutes,  except  in  the  first,  where  it  remains  only  long  enough 
to  have  the  unfixed  carmin  washed  away.  From  the  last  alcohol 
it  goes  into  oil  of  cloves  (or  benzol),  where  it  should  remain 
long  enough  to  become  perfectly  transparent.  It  is  then  to  l>e 
mounted  in  balsam. 

96.  Double-staining  can  also  be  effected  by  the  successive  use 
of  hsematoxylin  and  an  anilin  color.     By  the  use  of  two  or  more 
anilin  dyes  different  parts  of  a  specimen  may  be  colored  differ- 
ently ;  but  as  a  rule  all  these  effects  are  uncertain,  and  cannot  be 
relied  upon  for  the  positive  identification  of  tissues.     In  general, 
however,  long  bast  fibres  take  characteristic  colors. 

97.  The  following  combinations  for  double-staining  are  rec- 
ommended by  Dr.  Stirling,1  and  though  originally  designed  only 
for  animal  tissues,  serve  well  with  sections  of  plants :  — 

1.  Osmic  acid  and  picrocannin.  2.  Picric  acid  and  piero- 
carmin.  3.  Picrocarmin  and  logwood  (htematoxylin).  4.  Pi- 
crocarmin  and  an  anilin  dye.  />.  Logwood  and  iodine  green. 
6.  Eosin  and  iodine  green.  7.  Eosin  and  logwood.  8.  Gold 
chloride  and  an  anilin  dye. 

98.  In  the  cases  which  require  special  treatment,  for  instance, 
the  staining  of  the  nucleus,  the  precautions  laid  down   must 
be  attended  to  in  order  to  insure  success.     But  in  the  ordinary 
instances  where  it  is  desirable  to  stain  a  specimen  merely  to 
bring  some  part  into  prominence  for  purposes  of  demonstration, 
the  widest  choice  in  dyes  and  their  use  is  advised.     A  few  mor- 
dants have  been  tried  in  order  to  fix  the  colors,  but  with  little 
success.    The  best  are  tannin  in  solution,  and  aqueous  solutions 
of  any  of  the  alums.     A  little  practice  will  show  which  mordant 
is  best  for  each  case. 

99.  Specimens  stained  by  nearly  all  of  the  above  dyes  can 
be  mounted  securely  in  balsam,  as  directed  in  section  110;  but 
glycerin  and  glycerin-jelly  mounts  are  apt  to  become  faded  or 
discolored  after  a  time. 

100.  Mounting-media.     Pollen  and  other  dry  specimens  are 
served  in  shallow  cells  formed  by  a  thin  ring  of  asphalt- 

1  Journ.  Anat.  aqd  Phys.,  1881,  p.  34$, 


INTRODUCTION.  21 

cement,  varnish,  or  white  lead,  allowed  to  dry  nearly  to  hardness, 
upon  which  a  cover-glass  fits  firmly,  and  is  retained  by  a  second 
ring  of  the  same  cement.  If  the  precaution  is  taken  to  have  the 
cover-glass  fit  even!}'  to  the  first  layer  of  cement,  there  is  little 
danger  that  the  subsequent  layer,  which  is  to  hold  the  cover  in 
place,  will  creep  under  it  and  into  the  cell. 

101.  Glycerin,  pure  water,  calcic  chloride  solution,  potassic 
acetate,  and  like  liquids  may  be  used  as  mounting-media  in  cells 
prepared  in  the  manner  just  mentioned,  but  made  of  greater 
thickness.     Care  must  be  observed  to  avoid  touching  the  upper 
edge  of  the  cement  ring  with  the  liquid  ;   and  yet  the  cell  must 
be  completely  filled,  in  order  to  exclude  air. 

102.  If  a  specimen  has  been  prepared  in  glycerin,  and  it  is 
not  considered  well  to  disturb  the  cover-glass,  a  cement  ring  or 
square  can  be  built  up  around  the  cover  at  a  little  distance  from 
it,  provided  the  glass  slide  is  thoroughly  cleaned  at  the  place 
where  the  cement  is  to  be  put.     After  the  requisite  number  of 
layers  have  hardened  sufficiently,  a  ring  of  the  same  or,  better, 
of  a  more  quickly  drying  cement  may  be  placed  across  from  the 
edge  of  the  cell  to  the  co\er-glass,  to  hold  it  in  place.     As  this, 
in  drying,  will  contract  somewhat,  it  is  a  good  plan  to  place  two 
or  three  fragments  of  thin  glass  under  the  cover,  that  these 
ma}'  receive  the  pressure  and  prevent  crushing  the  specimen. 

103.  Of  the  mounting-media,  one  of  the  best  is  glycerin  and 
acetic  acid  in  equal  parts,  boiled  and  filtered.     It  serves  well  for 
thin-walled  specimens  (especially  in  the  lower  plants). 

104.  Specimens  of  fresh  cells  or  of  juicy  tissues  which  are  to 
be  mounted  in  glycerin  are  best  treated  in  the  manner  recom- 
mended by  Beale.1     tk  The  specimen  is  first  immersed  in  weak 
glycerin,  and  the  density  of  the  fluid  is  gradually  increased, 
either  by  adding  from  time  to  time  a  few  drops  of  strong  gly- 
cerin, until  it  bears  the  strongest,  or  by  allowing  the  original 
weak  solution  to  become  gradually  concentrated  by  slow  evapo- 
ration.    In  this  way,  in  the  course  of  two  or  three  days  the 
softest   and  most  delicate  tissues  may  be  made  to  swell  out 
almost  to  their  original  volume  in  the  densest  glycerin  or  syrup. 
They  become  more  transparent,  but  no  chemical  alteration  is 
produced,  and  the  addition  of  water  will  at  an}'  time  cause  the 
specimen  to  assume  its  ordinary  characters." 

105.  It  is  plain  that  mounts  in  any  liquid  must  be  liable  to 
injury  from  displacement  of  the  cover-glass ;    but  this  can  be 

1  How  to  Work  with  the  Microscope,  p.  360. 


22  INTRODUCTION. 

partially  guarded  against  by  fastening  to  the  upper  surface  of 
the  slide,  near  its  two  ends,  square  pieces  of  pasteboard  a  little 
thicker  than  the  cell  itself. 

106.  Glycerin-jelly,  a  mixture  of  glycerin  with  pure  gelatin,  is 
liquid  at  the  temperature  of  boiling  water,  and  solidifies  again 
on  cooling.   Any  specimen  which  is  not  injured  by  being  slightly 
heated  can  be  mounted  satisfactorily  in  the  jelly,  provided  it 
is  first  thoroughly  saturated  with  glycerin.     But  this  precaution 
is  by  no  means  necessary  in  all  cases. 

107.  A  drop  of  the  melted  jelly,  free  from  air-bubbles,  is 
placed  on  the  slide  (a  fragment  of  the  solid  jelly  can  be  melted 
on  the  slide  if  preferred),  the  specimen  placed  therein,  and  the 
cover-glass,  previously  moistened  slightly  on  the  under  side  with 
glycerin,  is  carefully  laid  on,  and  the  preparation  now  allowed 
to  cool.     When  the  jelly  is  again  hard,  a  varnish  or  cement  ring 
may  be  placed  around  the  edge  of  the  cover  to  hold  it  in  place. 
Asphalt-cement  is  apt  to  impart  to  the  jelly  a  dark  tinge,  which 
ma\T  sooner  or  later  spoil  the  mount,  and  hence  the  colorless 
varnishes  are  better. 

108.  The  edge  of  the  jelly  may  be  lightly   touched  with  a 
strong  solution  of  a  chromate,  for  instance,  bichromate  of  potas- 
sium, and  exposed  for  a  while  to  light.     This  renders  the  jelly 
insoluble,  and  firmly  sets  it. 

109.  The  following  are  among  the  best  formulas  for  making 
this  useful  mounting-medium  :  — 

One  part  of  pure  gelatin,  three  parts  of  water,  and  four  of 
glycerin  (Schacht,  quoted  by  Dippel).  Xordstedt  uses  the  same 
proportions,  and  advises  the  addition  of  a  small  piece  of  cam- 
phor or  a  drop  of  carbolic  acid,  to  prevent  moulding. 

One  part  of  gelatin  is  soaked  in  six  parts  of  water  for  two 
hours,  seven  parts  of  glycerin  are  added,  and  one  per  cent  of 
carbolic  acid  is  added  to  the  whole.  The  mass  is  heated  for 
fifteen  minutes,  with  constant  stirring,  and  then  filtered  through 
glass-wool.  All  the  ingredients  must  be  absolutely  pure  (Kaiser, 
Bot.  Centrbl.,  1880,  p.  2f>). 

The  proportions  employed  in  the  second  formula,  but  without 
the  addition  of  the  carbolic  acid,  give  a  clearer  jelly  ;  and  it  has 
not  been  apt  to  mould,  especially  if  the  cork  of  the  bottle  con- 
taining it  be  wrapped  in  a  thin  piece  of  linen,  which  has  been 
dipped  in  dilute;  carbolic  acid. 

110.  Canada  balsam.    This  is  used  either  (1)  alone,  or  (2)  in 
solution.     In  either  case  the  specimen  must  be  free  from  water, 
and  permeated  by  some  liquid  easily  miscible  with  the  balsam 


INTRODUCTION.  23 

This  is  easily  effected  by  first  saturating  the  object  with  alcohol 
(beginning  preferably  with  dilute,  and  then  using  stronger),  in 
order  to  expel  all  water ;  next  placing  the  alcoholic  specimen 
in  oil  of  cloves,  turpentine,  or  benzol,  until  the  alcohol  is  in 
turn  expelled.  The  specimen  thus  permeated  is  transferred  to 
balsam  which  has  been  previously  placed  on  the  slide.  Care 
must  always  be  taken  to  have  the  balsam  perfectly  free  from 
air-bubbles. 

111.  When  used  alone,   the   balsam   on   the   slide    ma}'   bo 
heated,  to  drive  off  a  part  of  its  more  volatile  constituents,  and 
the  specimen  can  then  be  placed  in  the  warm  liquid.     But  this 
method  is  not  applicable  when  the  specimen  is  affected  by  slight 
heating ;  it  is  best  adapted  to  hard  tissues,  like  woods  and  fibres. 
Balsam  which  has  thus  been  heated  hardens  on  cooling  to  a  good 
degree  of  firmness.     This  firmness  is  secured  with  balsam  used 
without  heat  only  after  a  longer  lapse  of  time,  during  which  the 
more  volatile  matters  have  escaped. 

112.  If  pure  balsam  is  cautiously  heated  in  a  capsule  until  it 
no  longer  gives  off  vapors,  the  melted  mass  will  cool  into  a  pale 
amber-colored  solid.     This  solid  dissolved  in  a  small  quantity  of 
benzol  forms  a  liquid  of  the  consistence  of  syrup,  which  is  useful 
for  all  mounting  where  heat  is  injurious.     The  specimens  must 
be  treated  successively  with  alcohol  and  benzol,  and  the}'  are 
then  ready  to  be  immersed  in  the  benzol-balsam  on  the  slide. 
An  equally  serviceable  solution  is  made  by  dissolving  the  mass 
in  chloroform.     Chloroform-balsam  requires  the  specimen  to  be 
saturated  with  chloroform  before  immersion. 

113.  In  all  the  above  cases  two  precautions  will  save  disap- 
pointment :    1st.  the  slides  and  cover-glasses  should  be  heated 
slightly,  to  drive  off  any  moisture  on  the  surfaces  which  are  to 
come  in  contact  with   the   mounting-medium ;    2d.   the  covers 
should  be  held  in  place  by  means  of  a  slight  weight,  or  by  the 
pressure  of  a  spring  clip,  until  the  balsam  or  its  solution  has 
become  tolerably  firm.     A  little  experience  will  show  that  speci- 
mens  mounted   in    balsam   may  require    a  somewhat  different 
management  of  the  mirror  under  the  stage  from  those  which  are 
mounted  in  a  medium  with  a  different  refractive  power.    Damar 
may  replace  balsam  when  the  latter,  which  is  the  better,  is  not 
to  be  had. 

114.  Hoyer's  mounting-media  are   highly  recommended  by 
Strasburger. '    The  one  which  is  preferred  for  anilin  preparations 

1  Das  botan.  Practicum,  1884,  p.  40. 


24  INTRODUCTION. 

is  made  by  adding  colorless  pieces  of  gum-arabic  to  a  solution 
of  potassic  acetate  or  ammonic  acetate,  until  the  liquid  becomes 
of  the  density  of  thick  syrup,  while  in  that  intended  for  carmin 
preparations  the  gum  is  dissolved  in  a  five  to  ten  per  cent 
aqueous  solution  of  chloral  hydrate,  and  about  ten  per  cent  of 
glycerin  added.  Either  of  these  media,  or  a  plain  solution  of 
pure  gum-arabic,  will  be  found  to  answer  admirably  for  all  prepa- 
rations of  woods  which  are  to  be  photographed. 

115.  The  edges  of  the  cover-glass  are  usually  painted  with 
some  varnish  of  good  quality.  Those  in  best  repute  are  :  — 

1.  Asphalt- varnish,  to  be  thinned  with  turpentine  when  too 
thick. 

2.  Maskenlack,  a  German  preparation,  thinned  with  alcohol. 

3.  Mikroskopirlack,  also  thinned  with  absolute  alcohol. 

4.  Shell-lac  in  alcohol,  tinged  with  some  anilin  color.     If  a 
few  drops  of  castor-oil  are  added  to  the  solution,  it  dries  into 
a  less  brittle  finish. 

5.  Gold-size. 

6.  White  lead  (with  oil). 

It  is  a  good  plan  to  revarnish  slides  whenever  the  varnish 
first  shows  any  indication  of  breaking  away. 

A  few  works  in  regard  to  microscopic  manipulation  and 
micro-chemistry  which  may  be  advantageously  consulted  by  the 
student  are  the  following :  — 

BEALE.  How  to  Work  with  the  Microscope  (London).  This  is  a  large 
octavo  volume,  with  very  minute  descriptions  of  microscopical  appliances  and 
manipulation.  Several  editions  have  been  printed. 

CARPENTER.  The  Microscope  (London).  A  small  octavo  of  about  900  pp. 
This  work  deals  at  some  length  with  the  structure  of  animals  and  plants. 

BEHEENS.  Hilfsbuch  zur  Ausfiihrung  Mikroskopischer  Untereuchungen 
im  Botanischen  Laboratorium  (Braunschweig,  1883).  This  is  specially  de- 
voted to  microscopic  manipulation  and  micro-chemistry.  An  English  trans- 
lation has  appeared. 

POULSEN.  Botanical  Micro-Chemistry.  Translated  and  enlarged  by  Pro- 
fessor Wm.  Trelease  (Boston,  1884).  An  excellent  account  of  the  chemicals 
used  in  the  examination  of  vegetable  structures,  together  with  some  directions 
for  their  employment. 

STRASBURGER.  Das  botanische  Practicum.  See  an  account  of  this  work 
on  page  165. 

BOWER  AND  VINES.  A  Course  of  Practical  Instruction  in  Botany  (Ixmdon, 
1885).  A  most  useful  and  convenient  guide  to  the  study  of  the  histology  of 
flowering  plants,  ferns,  and  their  allies. 


PART   L 


CHAPTER  I. 

THE  VEGETABLE  CELL  IN  GENERAL  :    ITS  STUCTUBE,  COM- 
POSITION,  AND   PRINCIPAL  CONTENTS. 

116.  The  unit  in  Vegetable  Anatomy,  the  fundamental  compo- 
nent of  which  the  fabric  of  plants  is  constructed,  and  from  which 
all  the  diverse  histological  elements  are  derived,  is  the  cell. 
Even  the  elements  which  are  the  least  cellular  in  appearance, 
and  which  have  names  of  their  own  (as  fibres,  ducts,  etc.),  are 
only  transformed  cells,  or  simple  combinations  of  them  ;  so  that 
the  cell  is  the  type  as  well  as  the  unit  of  vegetable  structure, 
as  indeed  it  is  of  animal  structure  also.  The  name  cell  is  one 
which  would  not  be  given  to  it  if  the  nomenclature  were  to  be 
founded  upon  our  present  knowledge.  Cells  were  originally 
taken  to  be  only  closed  cavities  in  a  vegetable  mass.1  We  now 

1  The  earliest  recognition  of  cellular  structure  in  plants  appears  in  Robert 
Hooke's  Micrograph!*  (1665),  p.  113.  "Our  microscope  informs  us  that 
the  substance  of  cork  is  altogether  fill'd  with  air,  and  that  that  air  is  perfectly 
enclosed  in  little  boxes  or  cells  distinct  from  one  another." 

Nehemiah  Grew,  of  London  (The  Anatomy  of  Plants,  book  i.  p.  4),  under 
date  of  1671,  says  of  the  mass  through  which  the  framework  of  a  young 
plant  is  distributed,  "It  is  a  Body  very  curiously  organiz'd,  consisting  of  an 
infinite  number  of  extreme  small  bladders,"  etc. 

Malpighi,  of  Bologna,  in  a  work  presented  to  the  Royal  Society  in  the  same 
year,  uses  nearly  the  same  language:  "Exterior  etenim  cuticula  utriculis,  seu 
sai'culis  horizontal!  online  locatis,  ita  ut  annulus  efformetur,  componitur,  etc." 
(Anatomes  Plantarum  Idea,  p.  2). 

As  a  preliminary  study,  a  beginner  should  prepare  and  examine  a  few  sec- 
tions like  the  following  :  — 

(1)  From  the  tip  of  the  root  of  a  bean  (which  has  germinated  on  wet  sponge 
or  paper)  cut  a  thin  section  lengthwise,  and  carefully  examine  it  under  a 
power  of  200-400  diameters.  If  the  section  is  thin  enough,  the  contents  of  the 
cells  can  be  made  out,  and  will  be  seen  to  consist  of  a  colorless  lining  (proto- 
plasm), in  which  one  part  (the  nucleus)  appears  denser  than  the  rest.  Next, 
treat  the  section  with  a  solution  of  iodine,  and  notice  what  parts  are  colored, — 
the  protoplasm  and  nucleus  are  yellow  and  brown,  but  the  cells  on  the  looser 
part  of  the  tip  contain  bluish  granules  (starch).  This  starch  can  best  be  shown 
by  first  dissolving  out  the  protoplasm  with  dilute  potash. 


26  THE   VEGETABLE  CELL   IN   GENERAL. 

know  them  to  be  organs  and  even  organisms.      Histology  there- 
fore begins  with  the  cell  in  its  independent  condition. 

117.  A  complete  and  living  vegetable  cell  consists  of  a  cell- 
wall  enclosing  certain  essential  contents. 

118.  In  their  earliest  state  some  of  the  lower  plants  exist  as 
a  mass  of  motile  living  matter,  not  bounded  by  any  envelope. 
But  in  all  plants  of  the  higher  grades  the  living  matter  of  the 
cell  is  from  the  very  first  protected  by  a  cell- wall. 

119.  That  which  is  essential  to  the  vital  activity  of  a  cell  is  an 
apparently  half-solid  substance,  —  protoplasm.     With  the  prop- 
erties of  protoplasm  as  a  living  thing.  Physiology  and  not  His- 
tology is  immediately  concerned.    But  it  is  necessary  throughout 
the  Itudy  of  Histology  to  make  a  distinction  between  the  cells 
which  are  vitally  active  and  those  which  serve  chiefly  or  wholly 
some  mechanical  end ;  and  hence  attention  must  be  called  at  the 
outset  to  the  means  by  which  the  living  matter  of  the  cell  can  be 
identified. 

120.  Protoplasm  exists  in  all  young  "cells  —  for  instance,  in 
the  soft  cone  of  tissue  in  buds,  in  root-tips,  and  other  points  of 
growth  —  as  a  nearly  transparent  or  finely  granular  substance.1 
It  completely  fills  the  interior  of  very  young  cells,  but  with 
increase  of  the  cells  in  size  there  arise  cavities  (vacuoles)  con- 
taining sap,  and  these  by  their  enlargement  and  continence  may 
appear  to  occupy  the  entire  space  within  the  cell.     If,  however, 
such  a  cell  be  acted  upon  by  anything  which  causes  contraction 


(2)  Make  a  thin  section  through  the  petiole  of  a  begonia  or  some  common 
house-plant,  and  observe  the  granules  imbedded  in  the  protoplasm  (chlorophyll- 
yranules) ;  notice  also  crystals,  either  in  masses  or  single. 

(3)  Examine  a  thin  section  through  diy  pine  wood,  test  with  iodine,  and 
observe  the  absence  of  protoplasmic  matters.      Examine  in  the  same  way  any 
hard  wood. 

(4)  Make  a  section  through  any  starchy  seed,  for  instance  a  common  bean, 
and  treat  it  with  a  solution  of  iodine  ;  notice  the  distribution  of  protoplasmic 
matters  in  the  form  of  thin  irregular  films  throughout  the  cells.     Examine  a 
similar  section  in  oil,  and  see  what  differences,  if  any,  can  be  detected.     Prob- 
ably the  presence  of  protein  granules  will  be  made  out 

From  these  preliminary  examinations  a  beginner  will  have  demonstrated 
the  protoplasmic  matter  in  its' active,  resting,  and  reserve  states  ;  he  will  have 
seen  chlorophyll,  the  nucleus,  and  starch,  the  chief  form  in  which  food  is 
stored  in  plants.  He  will  also  have  seen  a  few  of  the  more  common  crystals. 

After  such  a  study  the  student  is  urged  to  examine  practically  the  charac- 
teristics of  the  cell-wall  and  the  cell-contents  as  they  are  presented  in  this 
chapter. 

1  By  the  use  of  staining  agents,  especially  hsematoxylin,  protoplasm  can  in 
many  cases  be  shown  to  possess  a  complicated  mesh  of  very  delicate  fibres, 


PROTOPLASM. 


27 


of  the  protoplasm,1  us,  for  instance,  a  solution  of  common  salt, 
the  protoplasm  separates  from  the  cell-wall,  and  by  its  con- 
traction   shows    clearly    that    it    is    a 
closed  sac.     At  a  later  stage 
in  some  cells  even  this  thin 
protoplasmic  sac  wholly  dis- 
appears. 

121.  Protoplasm  itself  must 
be    regarded    as    essentially 
transparent  and  colorless,  but 
it  is   seldom   found   without 
some  admixture  of  other  mat- 
ters, which  give  it  a  granular 
appearance.      The    granules 
are  generally  very  small,  and 
as  a  rule  are  not  found  at  the 
periphery  of  the  mass.     The 
limiting  surface  of  the  proto-          2 
plasmic  mass  is  further  dis- 
tinguished by  being  somewhat  denser  and  firmer  than  the  sub- 
stance it  encloses ;   and  although  it  cannot  be  separated  from 
the  latter  by  mechanical  means,  it  is  often  spoken  of  as  a  film;" 

which  take  up  the  coloring  matter  readily,  leaving  the  remainder  of  the  mass 
unstained.  It  is  believed  by  Schmitz  that  the  unstained  mass  is  a  homoge- 
neous liquid  filling  the  meshes  (Sitzungsber.  der  niederrhein.  Gesellschaft  in 
Bonn,  1880). 

1  Such  substances  are  termed  plasiiwlytic  agents. 

8  Of  the  appearance  of  protoplasm,  the  following  remarks  by  Mohl,  who  first 
gave  it  the  name  in  1846,  are  of  interest.  "  If  a  tissue  composed  of  young  cells 
be  left  some  time  in  alcohol,  or  treated  with  nitric  or  muriatic  acid,  a  very 
thin,  finely  granular  membrane  becomes  detached  from  the  inside  of  the  wall 
of  the  cell  in  the  form  of  a  closed  vesicle,  which  becomes  more  or  less  con- 
tracted, and  consequently  removes  all  the  contents  of  the  cell,  which  are 
enclosed  in  this  vesicle,  from  the  wall  of  the  cell.  Reasons  hereafter  to  be 
discussed  have  led  me  to  call  this  inner  cell  the  primordial  utricle.  .  :  .  In 
the  centre  of  the  young  cell,  with  rare  exceptions,  lies  the  so-called  nucleus 
Cflluloe  of  Robert  Brown.  .  .  .  The  remainder  of  the  cell  is  more  or  less 
densely  filled  with  an  opaijue,  viscid  fluid  of  a  white  colour,  having  granules 
intermingled  in  it,  which  fluid  I  call  protoplasm  "  (Mohl:  The  Vegetable  Cell, 
Henfrey's  Translation,  1852,  pp.  36,  37). 

FIG.  1.  From  developing  anther  of  Orchis  raacubita.  showing  young  cells  com- 
pletely filled  with  protoplasm.  Observe  also  the  nucleus  with  its  nucleolus,  in  each 
cell.  (Guignard. ) 

FIG.  2.  A  hair  from  the  stamen  of  Tradescantia  pilosa.  showing  the  protoplasm  in 
the  form  of  granular  threads  running  from  side  to  side  of  the  cell-cavity.  The  white 
•paces  between  these  threads  are  vacaoles.  The  nucleus  can  also  be  seen  in  each  of  the 
four  cells  (Jacobs.) 


Og  THE    VEGETABLE   CELL   IN   GENERAL. 

and  where  there  is  any  break  in  the  continuity  of  the  mass,  for 
instance  in  the  case  of  sap-cavities,  a  similar  limiting  film  may 
be  supposed  to  exist. 

122.  The  consistence  of  protoplasm  depends  on  the  amount 
of  water  which  it  contains.     Thus  in  dry  seeds  it  is  nearly  as 
tough  as  horn,  while  in  the  same  seeds  during  germination  it 
becomes  like  softened  gelatin.     It  absorbs  water  readily  and  be- 
comes permeated  by  it,  thereby  increasing  its  apparent  fluidity, 
but  it  never  becomes  a  true  fluid.     Moreover,  there  is  a  limit 
to  the  amount  of  water  which  it  takes  up. 

123.  Chemically  considered,  protoplasm  is  a  very  complex 
substance.    It  belongs  to  a  group  of  bodies  of  which  the  albumin 
of  egg  may  be  conveniently  taken  as  the  type.     They  undergo 
many  slight  but  sometimes  remarkable  changes,  and  have  been 
collectively  termed  proteids.     The  terms  albuminoid*  and  pro- 
teids  may  be  used  interchangeably   (see  857). 

124.  The  albuminoids,  or  proteids,  which  form  with  water  the 
bulk  of  protoplasm  proper,  are  of  course  associated  with  the 
matters  which  this  living  substance  makes,  uses,  and  discards. 
But  these  matters  exist  in  the  protoplasm  in  very  different  pro- 
portions at  different  times,  though  never  in  such  amount  as  to 
obscure  the  peculiar  reactions  of  the  albuminoids.      These  are 
the  following :    1 .  The  yellow  or  brownish  color  imparted  by 
solutions  of  iodine.     2.    The  purple  color  produced  when  the 
specimen  first  saturated  with  a  solution  of  cupric  sulphate  is 
acted  on  by  potassic  hydrate.     3.    The  rose  color,  often  faint, 
which  follows    the    successive   action   of  a   solution   of  sugar 
and  strong  sulphuric  acid.     4.    The  red  color  given  by  Millon's 
reagent.    This  test  generally  requires  the  cautious  application  of 
heat.     5.  The  yellow  or  orange  color  following  the  application, 
in  succession,  of  strong  nitric  acid  and  ammonic  hydrate. 

125.  Dilute  solutions  of  the  caustic  alkalies  dissolve  proto- 
plasm ;  concentrated  solutions  do  not.     If  a  young  cell  is  acted 
on  by  concentrated   potash,  its  protoplasm  is  not  essentially 
affected ;  but  if  water  is  now  added,  the  protoplasm  dissolves 
at  once. 

126.  The  spherical  or  ellipsoidal  mass  found  in  the  protoplasm 
of  active  cells,  and  differing  from  the  rest  of  the  protoplasm  in 

ts  greater  density,  is  the  nucleus.  The  sharply  defined  point 
oftenseen  in  the  nucleus  is  the  nudeolus. 

127.  The  nucleus  undergoes  remarkable  changes  during  the 
earliest  stages  of  the  cell,  which  will  be  described  in  the  chapter 
on  "Growth."    The  relations  which  exist  between  the  proto- 


THE   CELL- WALL 


29 


plasm  in  one  cell  with  that  in  contiguous  cells  will  be  considered 
in  Chapter  VI. 

128.  The  cell-wall.     The  cell-wall  is  produced  from  materials 
contained  in  protoplasm.1  and  is  laid  down  in  intimate  contact 
with  it,  as  an  even  homogeneous  film  which  exhibits  at  first  no 
obvious  structure,  but  with  increase  in  size  generally  becomes 
modified  in  appearance,  consistence,  and  composition. 

129.  Its  evenness  of  surface  is  in  most  cases  early  lost  by 
addition  of  new  matter,  giving  rise  to  protuberances  or  markings 
of  different  sorts.     Though  at  first  possessing  no  evident  struc- 
ture, it  may  become  clearly  differentiated  into  layers,  and  thus 
become  stratified,  or  striations  may  appear.     Its  consistence,  at 
the  outset  that  of  the  most  delicate  bleached  linen  fibre,  may 
soon  become  changed,  on  the  one  hand  to  that  of  soft  gelatin, 
or  on  the  other  to  that  of  the  densest  wood.    Moreover,  although 
devoid  of  color  when  first  produced,  it  ma}*  acquire  distinct  color- 
ation ;  and,  lastby,  its  chemical  character  may  undergo  such  im- 
portant changes  that  its  normal  reactions  are  no  longer  given. 

130.  The  markings  of  the  cell-wall.     Uniform  thickening  of 
the  whole  cell-wall  is  extremely  rare ;  even  in  the  examples 
which  are  commonly  given  to  illustrate  it,  pores  or  channels, 
more  or  less  distinctly  visible,  interrupt 

its  continuity. 

131.  The   thickenings   may    possess 
great  irregularity,  or  they  may  be  so 
strictly  localized  and  regular  as  to  form 
characteristic  features  of  the  widest  use 
in  diagnosis.      They  may  project  out- 
wardly,    forming    ridges,    spines,    and 
other  sculpturings  ;  or,  as  is  most  com- 
monly the  case,  inwardly,  giving  rise 
to  rings,  spirals,  etc. 

132.  If  the  wall  is  thickened  through- 
out, except  at  well-defined  points,  de- 
pressions or  pits  are  produced,  varying 
considerably  in  outline,  but  occurring 
generally  as  simple  dots  or  lines.     In 

some  cases  it  is  not  difficult  to  see  that  these  dots  or  lines  are 
true  pores  or  fissures  running  from  one  cell  to  the  next. 

1  According  to  Schmitz,  the  cell-wall  is  produced  by  the  conversion  of  the 
limiting  film  of  protoplasm  into  cellulose.  That  the  cell-wall  is  formed  at  the 
limiting  film  admits  of  no  question. 

Fio.  3.    Pitted  duct;  from  stem  of  Clchorlnm  Intybua.    ( Jacobt.) 


30 


THE    VEGETABLE   CELL    IN   GENERAL. 


133.  Bordered  pits  are  a  very  common  modification  of  the 
last.     A  comparatively  large   spot   remains    unthickened,  but 
becomes  covered  by  a  low  dome  which  has  at  its  top  a  small 
aperture  ;  at  a  corresponding  point  of  the  wall  of  the  neighbor- 
ing cell  another  thickening  produces  a  similar  dome,  so  that  the 
two  domes  constitute  a  double  convex  body  which  appears  as 
a  disc  with  a  central  perforation.    These  bodies  are  known  as 
discoid  markings. 

134.  Sometimes  the  spot  covered  by  the  arched  projection  or 
dome  is  elliptical  instead  of  round.     When  this  kind  of  marking 
becomes  linear,  or  nearly  so,  it  is  termed  scalarifonn. 

135.  When  annular  and  spiral  thickenings  occur  the  cell-wall 
lying  between  them  remains  so  thin  that  a  slight  strain   suf- 

fices to  break  it,  releasing  the  rings 
and  coils.  The  number,  the  direc- 
tion, and  the  steepness  of  the  spi- 
rals furnish  in  some  cases  diagnostic 
features. 

136.  Besides    spirals    and    rings, 
there  are  intermediate  forms,  which 
pass  easily  over  into  netted  or  reticu- 
lated thickenings.     It  happens  some- 
times that  the  reticulated   markings 
are  so  regular  that  their  interspaces 
appear  as  regular  polygons. 

137.  The  external  sculpturing  of 
the   cell-wall   can   be  seen    in   many 
pollen-grains,    and   in    the    hairs   of 
many   plants,   though    in    the   latter 
case  the   projections,  may  be   partly 

4  due  to  irregularities  in  the   form  of 

the  coll. 

138.  Stratification  and  striation.  The  cell-wall,  even  at  an 
early  stage,  frequently  exhibits  a  distinctly  stratified  structure. 
In  some  cases,  at  least,  removal  of  all  the  water  which  forms  a 
constituent  of  the  wall  obliterates  every  trace  of  stratification, 
and  this  fact  supports  the  hypothesis  that  the  appearance  of 
lamination  is  caused  by  differences  in  the  amount  of  water  con- 
tained in  alternating  layers  of  the  wall.  The  less  strongly 
refractive  layers  are  supposed  to  contain  more  water  than  those 
whlch  are  m'ghly  refractive.  But  there  are  cases  of  stratification 


al  marklngs;  verUcal  "x^0"  ^rough  stem  of  Tradaacantla 


CELLULOSE.  31 

which  cannot  be  satisfactorily  explained  by  this  hypothesis. 
There  are,  besides,  numerous  instances  in  which  the  stratified 
appearance  is  not  clearly  shown  until  the  cell  has  been  acted 
on  by  an  acid  or  an  alkali ;  a  good  example  of  this  is  afforded 
by  the  firm  cells  of  the  albumen  of  the  vegetable  ivory  (Phy- 
telephas)  .* 

139.  An  appearance  of  spiral  striation,2  ascribed  also  to  the 
unequal  distribution  of  water,  is  often  seen,  especially  in  the 
cells  of  the  liber  of  Apocynacese  and  allied  orders,  and  in  many 
wood-cells.      The  striations  are  not  constant  as  regards  the 
steepness  of  the  spiral ;  in  fact,  in  a  few  instances  rings  instead 
of  spirals  are  present     A  striated  appearance  is  sometimes  pre- 
sented in  walls  which  have  been  deprived  of  all  their  water. 

140.  Chemically  considered,  the  young  cell-wall  consists  essen- 
tially of  cellulose,  a  substance  which  has  the  same  percentage 
composition  as  starch,  namely,  CtiIl,0O5.      Even  in  its  purest 
state  it  is  associated  with  a  trace  of  mineral   matters  which 
remain  behind  as  ash  when  it  is  burned,  and  in  the  living  cell  it 
is  always  permeated  by  water. 

141.  Cellulose  is  not  soluble  in  any  of  the  following  liquids 
commonly  used  in  microscopic  manipulations,  —  water,  alcohol, 
glycerin,  dilute  alkalies,  and  dilute  acids.     It  is,  however,  more 
or  less  strongly  acted  on  by  hot  concentrated  alkalies,  without 
passing  into  true  solution,  and   it  is  apparently  dissolved  by 
strong  sulphuric  acid.      Whether   cellulose   becomes   truly  dis- 
solved by  concentrated  sulphuric  acid,  or  merely  forms  some 
other  carbohydrate  under  its  action,  is  of  little  consequence,  so 
far  as  the  destruction  of  cell-walls  is  concerned.     In  nearly  all 
cases  its  action  is  so  energetic  that  the  wall  of  a  cell  can  be 


1  As  shown  by  Mohl,  the  action  of  a  mineral  acid  of  proper  degree  of  con- 
centration causes  the  wall  to  swell  up,  and  the  lamellar  structure  becomes 
very  distinct.      "  By  this  means  the  lamellar  structure  may  be  demonstrated 
even  in  those  cases  in  which  the  unaltered  membrane  appeared  completely 
homogeneous"  (Mohl:  Vegetable  Cell,  p.  10). 

2  ''The  stratification  is  visible  on  the  transverse  and  longitudinal  sections 
of  tlu>  cell-wall,  the  striation  on  the  surface  as  well  ;  it  is  usually  most  evident 
there,  but  is  in  general  less  easily  seen  than  the  stratification  ;  it  depends  on 
the  presence  of  alternately  more  or  less  dense  layers  in  the  cell-wall,  meeting 
its  surface  at  an  angle.     Generally  two  such  systems  of  layers  may  be  recog- 
nized mutually  intersecting  one  another.     There  are  thus  all  together  three 
systems  of  layers  present  in  cell-wall  :  one  concentric  with  the  surface,  tind  two 
vertical  or  oblique  to  it  mutually  intersecting,  like  the  cleavage  planes  of  a 
crystal  splitting  in  three  directions  (Nageli)  ;  and  just  as  this  cleavage  is  some- 
times more  evident  in  one  direction,  sometimes  in  another,  so  it  is  also  with 
the  stratification  and  striation  "  (Sachs:  Text-lxwk,  2d  Eng.  ed.,  p.  20). 


32  THE   VEGETABLE   CELL   IN   GENERAL. 

wholly  removed  by  this  acid,  even  without  destroying  the  proto- 
plasmic contents ;  and  this  fact  has  been  extensively  employed 
in  the  examination  of  the  continuit}'  of  the  protoplasm  in  con- 
tiguous cells.1 

142.  The  only  known  solvent  from  which  cellulose  can  be  re- 
covered without  change  of  composition  is  Schweizer's  reagent, 
ammoniacal   solution  of  cupric   oxide.     In   this   liquid,   cellu- 
lose swells  considerably,  and  slowly  disappears.     It  is  thought 
by  some  chemists  that  it  does  not  truly  dissolve.      From  its 
apparent  solution,  it  can  be  precipitated  in  the  form  of  a  florcu- 
lent  mass  by  acids,  salts  of  many  kinds,  and  oven  by  the  addi- 
tion of  a  large  amount  of  water  (see  55). 

143.  Freshly   prepared   aqueous   and   alcoholic   solutions   of 
iodine  do  not  color  pure  cellulose  beyond  giving  a  faint  yellow- 
ish tint ;  but  if  the  reagents  have  been  kept  for  some  time,  par- 
ticularly in  the  light,  they  may  impart  a  blue  color.2    The  latter 

1  Unsized,  well-bleached  linen  paper  is  nearly  pure  cellulose.     It'  it  is  dipped 
in  a  cold  mixture  of  one  volume  of  water  and  two  volumes  of  strong  sulphuric 
acid,  withdrawn  after  ten  to  twenty  seconds,  and  washed  thoroughly  in  water, 
and  finally  in  dilute  ammoniacal  water,  it  becomes  much  like  parchment.    This 
"vegetable  parchment"  is  a  suitable   membrane  for  certain  experiments  in 
absorption.     The  acid  in  this  experiment  is  supposed  to  convert  at  least  a 
portion  of  the  cellulose  into  a  substance  which  closely  resembles  starch  in  its 
chemical  reactions,  termed  amyloid.     Parchment  paper  can  be  made  also  by 
concentrated  zinc  chloride,  and  by  a  few  other  agents. 

2  Mohl  (The  Vegetable  Cell,  p.  24,   Eng.  Trans.)  says:    "When  imbued 
with  iodine,  it  becomes  indigo-blue  if  wetted  with  water."     In  a  note  on 
pages  28  and  29,  he  further  says:   "  My  researches  shewed  me  that  the  in- 
fluence of  sulphuric  acid  was  by  no  means  necessary  for  the  production  of  the 
blue  colour  in  membranes  which  are  not  strongly  incrusted,  as  in  the  paren- 
chymatous  cells  of  succulent  organs,  but  that  iodine  and  water  alone  are  suffi- 
cient; while  in  lull-grown  and  hardened  cells  sometimes  the  primary  membrane 
alone,  sometimes  even  a  greater  or  smaller  portion  of  the  secondary  layers  had 
through  the  deposition  of  foreign  substances,  altogether  lost  the  projierty  of 
becoming  blue  on  the  application  of  sulphuric  acid  and  iodine,  although  they 
were  still  composed  of  cellulose,  and  iodine  alone  would  very  readily  produce 
a  blue  colour  in  all  their  membranes  after  the  infiltrated  matters  had  been 
removed.     The  means  I  employed  to  remove  the  infiltrated  substances  were 
caustic  potash  and  nitric  acid.  .  .  .  After  this  treatment,  the  whole  of  the 
layers  of  all  elementary  organs  are  coloured  a  beautiful  blue  by  iodine  even 
when  they  offer  so  great  a  resistance  to  the  action  of  sulphuric  acid  before  the 
treatment  with  nitric,  as  is  the  case  in  the  outer  membrane  of  wood-cells  and 
of  vessels,  and  in  the  brown-cells  at  the  circumference  of  the  vascular  bundles 
in  Ferns." 

It  is  plain  that,  in  the  latter  cases,  the  cell-wall  had  been  very  powerfully 

ed  on  before  the  application  of  the  iodine,  ami  to  this  severe  preliminary 

treatmer    may  be  ascribed  the  efficiency  of  the  latter  in  producing  the  blue 


REACTIONS    OF   CELLULOSE.  33 

color,  however,  is  given  even  by  fresh  solutions  of  iodine  to 
cellulose  which  has  been  previously  treated  with  certain  chemi- 
cal agents,  for  instance,  strong  sulphuric  acid.  A  convenient 
method  of  employing  this  reaction  as  a  test  for  cellulose  is  to 
thoroughly  moisten  the  object  with  a  dilute  solution  of  iodine, 
and  then  to  apply  strong  sulphuric  acid,  upon  which  the  cellulose 
immediate!}'  turns  bright  blue.  It  is  sometimes  advantageous 
to  dilute  the  sulphuric  acid  employed,  either  with  water  or  with 
glycerin  ;  but  for  most  cases  the  concentrated  acid  is  the  best. 

Schulze's  solution  of  iodine,  better  known  as  chloroiodide  of 
zinc,  used  alone,  gives  with  pure  cellulose  a  blue  color  inclining 
to  purple.  This  reaction,  though  not  always  so  prompt  as  the 
other,  is  generally  more  manageable,  and,  on  the  whole,  more 
satisfactory. 

In  a  few  instances  the  cell-membrane  becomes  yellowish- 
brown  throughout,  upon  the  application  of  an  iodine  solution, 
a  reaction  which  might  be  easily  mistaken  for  that  which  albu- 
minoids give  ;  that  the  color,  however,  is  not  here  due  to  their 
presence,  appears  on  subjecting  the  tissue  to  the  action  of 
Millon's  reagent.  Vertical  sections  of  the  stem  of  Begonia,  as 
noticed  by  Nageli,  afford  an  instructive  example  of  this.1 


1  That  the  yellow  color  imparted  by  iodine  has  been  otherwise  interpret, 
will  ii|i|M-ar  from  the  following  :  — 

Harting(Ann.  des  Sc.  nat.,  ser.  3,  tome  v.  p.  328)  states,  that  "all  lignifitJ 
cells  have  Protein  matters  in  their  walls." 

Mohl  (The  Vegetable  Cell,  p.  25)  says:  "Nitrogenous  compounds  <Io  nci 
occur  in  the  membranes  of  cells  which  are  just  at  the  commencement  of  their 
development,  for  these  are  not  coloured  yellow  by  tincture  of  iodine,  yet  hardly 
a  full-grown  cell  is  met  with  in  which  this  is  not  the  case." 

It  is  held  by  Nageli  that  vegetable  cell-membranes  consist,  in  some  in- 
stances, of  two  isomeric  substances,  unequally  soluble,  which  are  intimately 
commingled.  One  of  these  is  soluble  in  cold  water,  more  easily  in  hot  water, 
and  sometimes  needs  for  its  complete  extraction  a  dilute  acid.  From  the  solu- 
tion iodine  throws  down  a  blue  or  bluish-green  precipitate. 

A  synoptical  table,  based  on  differences  in  solubility  of  cellulose  and  its 
modifications,  and  in  their  behavior  towards  iodine,  has  been  constructed  by 
Nageli.  The  part  of  the  table  which  is  given  below  affords  excellent  practice 
for  the  beginner. 

I.   DIFFERENCES  IN  SOLUBILITY. 

(1)  In  cold  water,  becoming  swollen  ;  in  hot  water,  disappearing,  vtqctaWe 
mucilage  ;  c.  </.,  in  the  outer  layer  of  the  cells  forming  the  testa  of  quince  seeds 
and  tJwse  of  flax, 

(2)  Soluble  in  concentrated  sulphuric  acid,  and  in  cuprammonia;  e.  g.t  cotton- 
hairs,  bast-fibres,  etc. 

3 


£4  THE   VEGETABLE   CELL    IN    GENERAL. 

144.  The  principal  modifications  of  the  cell- wall  are  the  fol- 

(1)  Partial  or  complete  conversion  into  mucilage  (Gelatina- 
tion)  ;  (2)  Lignification  ;  (3)  Cutinizatiou  (or  Suberification) ; 
(4)  Mineralization. 

145.  All  of  these,  except  the  first,  change  the  chemical  char- 
acter of  the  cell- wall  only  by  what  may  be  regarded  as  infiltra- 
tion ;  upon  removal  of  the  infiltrated  matter  by  means  of  proper 
agents,  the  cellulose  basis  of  the  wall  is  left  behind  with  very 
little  if  any  change. 

146.  It  sometimes  happens  that  one  part  of  the  membrane  of 
a  cell,  or  even  one  of  its  layers,  may  be  modified  in  one  way,  and 
another  in  another ;  it  is  also  possible  for  the  same  membrane  to 
undergo  two  of  the  changes  above  mentioned  ;  namely,  Lignifi- 
cation and  Mineralization. 

147.  The  mucilaginous  modification.   Commonh"  the  cell-wall  is 
not  much  changed  by  immersion  in  water.    It  may  become  more 
nearly  transparent,  but  its  size  and  density  are  not  essentially 


(3)  Soluble  in  sulphuric  acid,  insoluble  in  cuprammonia  (unless  previously 
acted  on  by  acids  or  alkalies)  ;  e.  g.,  the  pith,  and  medullary  rays  of  woods. 

(4)  Soluble  in  concentrated  sulphuric  acid  ;  insoluble  in  cupranimonia,  but 
becoming  soluble  in  this  upon  previous  treatment  with  Schulze's  macerating 
liquid  ;  c.  g.,  wood-cells  of  pine,  oak,  yew,  etc. 

'5)  Insoluble  in  concentrated  sulphuric  acid  and  cuprammonia,  but  soluble 
in  boiling  concentrated  potassic  hydrate  ;  e.  g.,  cuticle,  and  the  outer  layer  of 
the  '"lembrane  of  older  ducts. 

II.  IODINE  REACTIONS. 

(1)  With  iodine  and  water,  a  blue  color  :  lichen-filaments,  etc. 

(2)  With  iodine  and  water,  no  color  ;  but  giving  a  blue  tint  with  iodine  and 
a  metallic  iodide  ;  or  when  iodine  is  followed  by  sulphuric  acid  :  — 

A.  Thin-walled  Parenchyma  (which  will  often  turn  blue  when  a  pure  iodine 
solution  acts  with  repeated  drying),  older  Parenchyma,  the  inner  part  of  thick- 
ened wood-cells  of  Pinus  and  Abies,  and  the  bast-fibres  of  hemp. 

B.  Only  when  the  reagents  have  been  preceded  by  the  application  of  nitric 
acid  :  all  membranes  in  the  interior  of  the  plant,  e.  g.,  the  outer  part  of  wood- 
cells  and  ducts,   the  brown  cells  which  surround  the  vascular  bundles  in 
ferns,  etc. 

C.  Only  when  the  reagents  have  been  preceded  by  the  use  of  boiling  potassic 
hydrate  :  cork,  etc. 

According  to  Fremy  and  Urbain,  the  substances  which  form  the  skeleton  of 
plants  are  principally  pectose  and  derivatives  from  it,  cellulose  and  its  isomers. 
•asculose,  and  cutose.  These  four  groups  are  thus  distinguished  from  one 

another. 

Pectose  acted  on  by  alkaline  carbonates  is  changed  into  pectic  acid,  and 


THE   MUCILAGINOUS   MODIFICATION.  35 

affected.  It  sometimes  happens,  however,  that  the  cell-wall 
acquires  wholly  new  relations  to  water,  and  becomes  capable  of 
absorbing  a  large  amount  of  it  with  great  increase  of  volume  and 
translucency.  A  cell-wall  which  has  undergone  this  mucilagi- 
nous modification  takes  on,  when  placed  in  water,  the  consist- 
ence of  soft  gelatin,  and  if  the  mass  is  then  warmed  it  appears 
to  dissolve,  forming  a  thick  mucilage.  Upon  drying,  the  muci- 
lage hardens  into  a  translucent  gum,  in  which  the  cellulose  char- 
acter is  nearly  or  wholly  lost. 

148.  Generally  the  changes  produced  in  such  a  wall  by  water 
are  so  rapid  that  it  is  desirable  to  place  the  specimen  at  first  in 
alcohol,  and  then  to  replace  this  medium  cautiously  by  water  or 
by  dilute  glycerin,  when  the  variations  in  shape,  size,  and  con- 
sistence can  be  easily  followed.     The  addition  of  alcohol  will  of 
course  arrest  the  changes  at  an}-  stage  desired. 

149.  These  changes  can  be  easily  traced  in  the  outer  cells  of 
the  integument  of  a  flax-seed.      The  mucilage  appears  as  an 
obscurely  stratified  mass  nearly  filling  the  cells,  except  at  their 
centre,  where  there  is  a  low-arched  cavity.     On  the  cautious 


pectates  are  formed.  These  are  readily  decomposed  by  hydrochloric  acid,  and 
insoluble  gelatinous  pectic  acid  is  thrown  down. 

Cellulose  and  its  isomers  agree  in  being  soluble  in  concentrated  sulphuric 
acid,  but  they  differ  in  the  following  points  :  Cellulose  dissolves  at  once  in 
cuprammonia  ;  paracellulose,  only  after  the  action  of  acids  ;  metacellulose,  not 
even  then. 

Vasculose  is  not  easily  soluble  in  concentrated  sulphuric  acid,  but  after  the 
action  of  oxidizing  agents  gives  rise  to  resinous  acids,  which  are  separable  by 
alkalies  from  associated  cellulose. 

Cntose,  the  transparent  film  covering  the  aerial  organs  of  plants,  is  dissolved 
neither  by  concentrated  sulphuric  acid  nor  by  cupraminonia,  but  dissolves 
without  change  in  alkaline  liquids.  The  following  results  of  analyses  by  Fremy 
and  Urbain  (Ann.  Sc.  nat.  bot.,  1882)  show  approximately  the  amount  of 
these  substances  in  different  parts  of  certain  plants. 

Root  of  Paulmcnia.  —  (1)  Substances  soluble  in  water  and  in  dilute  alkalies  : 
cork  45,  soft  bast  56,  body  of  root  47.  (2)  Vasculose  :  cork  44,  soft  bast  34, 
body  of  root  17.  (3)  Paracellulose  :  cork  4,  soft  bast  4,  body  of  root  30. 

Stems.  —  Vasculose  increases  in  amount  with  the  density  of  the  wood.  The 
pith  contains  :  of  cellulose  37,  paracellulose  38,  vasculose  25  per  cent.  Cork 
contains  :  matters  soluble  in  acids  and  alkalies  5,  cutose  43,  vasculose  29, 
cellulose  and  paracellulose  12  per  cent  (cutose  and  vasculose  forming  together 
the  suberine  of  Chevreul). 

Leaves  of  Ivy. — Water  and  substances  soluble  in  neutral  solvents  707.7, 
parenchyma  (formed  of  cellulose  and  pectose)  240,  fibres  and  vessels  (of  vascu- 
lose and  paracellulose)  17.3,  epidermis  (cutose  and  paracvllulose)  35  parts. 

Petals  of  Dahlia,.  — Water  and  soluble  matters  961.30,  parenchyma  (of  cel- 
lulose and  pectose)  31.63,  vasculose  1.20,  paracellulose  2.27,  cutose  3.60  parts. 


36  THE  VEGETABLE   CELL   IN   GENERAL. 

addition  of  water,  this  cavity  becomes  more  clearly  defined,  the 

whole  mass  of  the  cell  swells,  and  the  mucilage  can  then  be 

made  out  as  a  distinctly 
stratified  structure  belong- 
ing apparently  as  much  to 
the  outer  as  to  the  inner 
face  of  the  cell-wall.  But 
if  the  action  of  water  is 
prolonged,  the  stratified  ap- 
pearance vanishes,  and  the 
wall  becomes  optically  ho- 
mogeneous, with  the  excep- 
tion of  its  middle  portion, 
the  so-called  primary  mem- 
brane, which  remains  un- 
changed. On  the  addition 
of  iodine  and  sulphuric 

acid,  the  primary  membrane,  but  not  the  mucilage,  becomes  blue. 

Furthermore,  the  lateral  walls  of  the  cells  are  not  converted 

into  mucilage. 

150.  The  mucilaginous  modification  can  be  examined  to  ad- 
vantage in  the  seeds  of  some  Polemoniaceae  (especially  Collomia) 
and  a  few  Acanthaceae,  e.  y.<  Ruellia.     These  seed-coats  are 
covered  with  hairs  which  break  open  when  wet,  and  allow  not 
only  the  mucilage  but  also  slender  coiled  threads   to   escape. 
The  achenes  of  some  Composite  of  the  Senecio  group  and  the 
nutlets  of  a  few  Labiate  (the  Salvia  tribe)  exhibit  nearly  the 
same  phenomenon. 

151.  Ligniflcation.      Induration   of   the   cell- wall   is   caused 
most  commonly  by   the   presence  of  an   incrusting   substance 
known  as  lignin.     Owing  to  the  difficulty  of  separating  it  from 
the  cellulose,  with  which  it  is  associated,  its  chemical  composi- 
tion must  be  regarded  as  uncertain.     Although  generally  spoken 
of  as  a  single  substance,  it  is  probable  that  the  lignin,  or  in- 
crusting  matter,  is  made  up  of  several  different  substances,1 

1  Payen  (Mem.  des  savants  etrangers,  ix.,  1846,  pp.  68,  5)  distinguished 
four  such  incrusting  matters,  differing  in  their  composition  and  in  their  l>e- 
havior  to  solvents.  Lignose:  insoluble  in  water,  alcohol,  ether,  and  ammo- 
nia; soluble  in  solutions  of  potassa  and  soda.  Lignone :  insoluble  in  water, 
alcohol,  and  ether ;  soluble  in  ammonia,  potassa,  and  soda.  Lignin :  in- 
soluble in  water  and  ether ;  soluble  in  alcohol,  ammonia,  potassa,  and  soda. 

FIG.  5.  Section  of  the  albumen  of  Ceratonia  siliqua,  showing  mucilaginous  modifica- 
tion. (Sacha.) 


LIGNIFICATION. 


37 


which  occur  in  different  proportions  in  different  plants  and  in 
different  parts  of  the  same  plant. 

152.  Lignin  dissolves  readily  in  Schulze's  macerating  liquid 
and    in    potassic  hydrate,  but  not  in  cuprararaonia,   the  well- 
known  solvent  for  cellulose. 

153.  By  the  use  of  Schulze's  macerating  liquid  a  lignified  cell- 
wall  can  be  wholly  freed  from  its  incrusting  substance,  and  pure 
cellulose  will  be  left  behind.     For  control,  it  is  well  to  employ 
the  tests  for  lignin  given  below,  both  with  ordinary  wood  and  with 
similar  specimens  which  have  been  treated  with  this  solvent. 

154.  Tests  for  lignin.      1.  Salts   of  anilin.      If  a  lignified 
cell-wall  is  subjected  to  the  action  of  a  strong  solution  of  anilin 
sulphate  acidulated  with  sulphuric  acid,  or  to  that  of  a  solution 
of  anilin  chloride  acidulated  with  Imlrochloric  acid,  it  will  at 
once  turn  yellow.     The  depth  of  the  color  depends  somewhat 
upon  the  strength  of  the  solution.     The  color  is  destroyed  by 
alkalies,  but  is  restored  by  acids.    Wiesner,  who  first  applied  the 
foregoing  reagents  to  the  detection  of  lignin,  has  suggested  an- 
other which  is  for  many  cases  even  more  satisfactory ;  namely, 
2.  Phloroglucin.     In   an   alcoholic   or  aqueous  solution  of  this 
substance  (.01  per  cent)  a  lignified  cell-wall  does  not  change 
color ;  but  if  the  specimen  is  slightly  acidulated  with  hydrochloric 
acid,  it  becomes  violet  or  purple.     3.  Carbolic  acid    (phenol) 
and  hydrochloric  acid.     The  solution  described  on  page  11  im- 
parts to  lignified  cell-walls,  when  exposed  to  a  strong  light,  a 
green  color  which  is  very  fugitive.    Specimens  under  examination 
should  therefore  be  watched  from  the  moment  that  the  reagent 
reaches  them.    4.  Indol.     An  aqueous  solution  is  to  be  replaced 
under  the  cover-glass,  after  it  has  moistened  the  specimen  thor- 
oughly, by  a  little  dilute  sulphuric  acid ;  lignified  cells  will  be- 
come red  or  reddish-violet.    This  reagent  does  not  appear  to  have 

Liqnirtose :  soluble  in  all  the  solvents  mentioned  above,  but  only  to  a  slight 
extent  in  water. 

CHEMICAL  COMPOSITION. 


Carbon. 

Hydrogen. 

Oxygen. 

Lignose 

46  10 

6  09 

47  81 

Lignone 

50  10 

5  82 

44.08 

Lignin   .                            .    .                       ... 

62  25 

593 

31  82 

Lignir&we 

6791 

689 

2520 

44.35 

6  14 

49  51 

According  to  Franz  Schulze,  the  probable  composition  of  lignin  is  :  Carbon 
55.55;   Hydrogen,  5.83;  Oxygen,  38.62. 


38  THE   VEGETABLE  CELL  IN   GENERAL. 

any  marked  advantage  over  that  which  gives  nearly  the  same 
color,  namely,  phloroglucin. 

155.  By  the  empk>3'iiient  of  these  reagents  many  cell-walls 
have  been  shown  to  be  distinctly  lignified  when  the  older  re- 
agent—  iodine  iu  solution  —  failed  to  detect  the  change. 

156.  Cutinization.   Ordinary  and  lignih'ed  cell-walls,  and  those 
which  have   undergone   the   mucilaginous  modification,  absorb 
water  freely.    On  the  other  hand,  the  walls  of  certain  cells  found 
chiefly  on  the  exterior  of  organs  are  repellent.     The  substance 
which  imparts  the  repellent  character  to  the  cell-wall  is  known 
as  cutin ;  when  restricted  to  cork  it  is  called  suberin. 

157.  Cutin  and  suberin  have  been  described  as  different  sub- 
stances ;  but  although  the  former  is  more  generally  associated  with 
waxy  matters,  its  reactions  are  essentially  the  same  as  those  of 
suberin.    The  water-proofing  of  the  cell-wall  ma}*  be  superficial, 
as  in  most  young  epidermal  cells,  or  it  may  affect  the  whole 
structure  of  the  wall,  as  in  the  case  of  cork.     If  a  distinction  is 
made  between  the  two  states,  the  first  ma}-  be  termed  cutiniza- 
tion,  the  second,  suberification. 

158.  Cutin  can  be  removed  from  the  walls  with  which  it  is 
associated,  by  the  use  of  Schulze's  macerating  liquid,  subsequent 
treatment  with  potassa,  and  careful  washing.     It  is  sometimes 
necessary  to  heat  the  section  in  potassa  before  the  cellulose  can 
be  completely  freed  from  the  other  matters. 

159.  Hohnel1  has  shown  that  the  wall  of  a  cork-cell,  with 
the  exception  of  the  }*oung  cork-cells  in  Coniferae,  is  composed  of 
five  plates:  (1)  a  middle  plate,  common  to  the  two  contiguous 
cells;  (2)  two  plates, one  on  each  side  of  the  latter,  consisting 
of  cellulose  which  is  both  cutinized  and  lignified  ;  (3)  two  plates 
of  cellulose  forming  the  inner  lining  of  the  respective  cells.    The 
latter  plates  may  be  more  or  less  lignified.     Differences  in  the 
relative  proportions  of  these  constituent  plates  give  rise  to  dif- 
ferences in  the  character  of  different  kinds  of  cork. 

160.  As  in  the  case  of  lignin,  the  difficulty  of  extracting  cutin 
renders  its  chemical  composition  doubtful.     It  is  usually  given 
as  follows :  — 

Carbon         73-74  per  cent 

Hydrogen 10  " 

Oxygen   17-16        " 

But  there  is  also  a  trace  of  nitrogenous  matter  demonstrable ; 
this  probably  belongs  to  residual  protein  matters  which  are  in 

*  Sitzungsber.  d.  k.  Akad.  Wien,  Bd.  Ixxvi  1  Abth. 


MINERALIZATION.  39 

the  cell-cavity,  and  not  in  the  cell-wall.  Sulphuric  acid  and 
chromic  acid,  even  when  concentrated,  produce  little  effect  on 
cutinized  membranes,  beyond  removing  traces  of  cellulose  pres- 
ent in  the  cell-wall.  The  latter  acid,  however,  increases  the 
transparency  of  cutinized  membranes,  especially  after  prolonged 
action. 

161.  Potassic   hydrate   softens  such  membranes  and   colors 
them  yellow  ;  when  heated  it  breaks  them  into  a  granular  mass 
which  may  be  removed  by  careful  washing.     Cautiously  heated 
with  Schulze's  macerating  liquid,  they  disintegrate  into  granules 
of  eerie  acid.  —  a  substance  which  dissolves  in  alcohol,  ether,  and 
benzol.     Several  of  the  coal-tar  colors  stain  the  cutinized  por- 
tions of  cell-walls  very  deeply ;  if  the  specimen  thus  colored  is 
placed  in  absolute   alcohol,  the  cutinized   parts   alone  remain 
colored.1     Two  points  relative  to  the  cutinization  of  epidermal 
cells  may  be  noted :   (1 )  the  cutin  may  take  on  the  form  of  lay- 
ers, often  numerous  and  conspicuous  ;   (2)  there  ma}-  be  a  con- 
siderable irregularity  in  the  outline  of  the  deposits,  sometimes 
as  folds,  hooks,  and  the  like,  which  do  not  strictly  conform  to 
the  cellulose  wall  on  which  the)-  arise. 

162.  Mineralization  of  the  cell-wall.    Although  all  cell-walls, 
even  the  most  delicate,  can  be  shown  to  contain  traces  of  inor- 
ganic matter,  it  is  only  in  a  few  special  cases  that  such  substances 
appear  in  a  form  to  be  noticed  under  the  microscope.     Minerali- 
zation of  the  wall  ma}-  be  general  or  local,  may  depend  upon 
the  presence  of  crystals  or  of  amorphous  deposits,  and  these  may 
consist  of  silicic  acid  or  of  calcium  salts. 

163.  General  mineralization  of  the  wall  depends  most  fre- 
quently on  silicic  acid,  and  may  be  best  demonstrated  by  first 
boiling  the  specimen  in  nitric  acid,  drying,  heating  to  redness  on 
platinum-foil,  and.  lastly,  treating  again  with  nitric  acid.     The 
silicic  acid  remains  behind  as  a  delicate  skeleton  which  copies  in 
all  particulars  the  contour  of  the  wall  of  which  it  formed  a  part. 
Fine  examples  are  afforded  by  the  harder  grasses.2 

Calcium  salts  may  exist  in  crystalline  or  amorphous  form,  and 
may  be  distinguished  by  the  tests  to  be  given  for  them  under 
the  section  on  "  Crystals."  That  in  some  cases  they  constitute 
an  integrant  part  of  the  wall  itself  admits  of  no  question. 

164.  Iq  the  cells  of  many  plants,  especially  Urticacese,  pedi- 
cellated  concretions  occur,  which,  on   superficial  examination, 

1  Olivier:  Bull.  Soc.  bot.  de  Fr.,  1880,  p.  234. 

a  Tabashetr  consists  of  the  siliceous  substances  which  occur  in  the  joints 
of  bamboo  in  large  quantities. 


40 


THE   VEGETABLE   CELL   IN    GENERAL. 


appear  to  be  much  like  the  sphere-crystals  described  in  186.  But 
if  they  are  carefully  treated  with  dilute  hydrochloric  acid,  the 
chief  part  of  the  concretion  disappears,  leaving  behind  a  delicate 
trace  of  cellulose  which  was  intermingled 
with  it.  That  this  cellulose  was  an  in- 
trusive growth  into  the  cell  from  the 
wall,  is  shown  by  a  study  of  its  develop- 
ment. In  most  cases  such  concretions 
(Cystoliths)  are  plainly  stalked,  but  in 
some  instances  they  are  only  obscurely 
stalked,  and  are  with  difficulty  distin- 
guished from  the  ordinary  cell  concre- 
tions. In  the  leaf  of  Ficus  elastica  (sec 
Fig.  6)  they  are  more  completely  devel- 
oped than  in  any  other  common  plant. 

165.  Other  changes,  chiefly  those  of 
degradation,  may  take  place  in  the  cell- 
wall,  giving  rise  to  products  variously 

known  as  gums,  resins,  &c. ;  but  in  all  these  cases  there  is  such 
a  commingling  of  the  cellulose  derivatives  with  those  formed 
from  the  contents  of  the  cell,  that  they  cannot  be  readily  dis- 
tinguished. 

166.  Protoplasm,  as  was  shown  in  the  previous  sections,  gives 
rise  upon  its  exterior  to  the  cell-wall.     Inside  the  cell,  likewise, 
it  produces,  either  directly  or  indirectly,  various  substances.     In 
the  present  chapter  these  substances  are  to  be  considered  only  so 
far  as  relates  to  their  detection  and  identification.    Most  of  them 
are  to  be  examined  later,  with  reference  to  their  office  in  the  life 
of  plants. 

167.  Plastids.    In  the  protoplasm  of  active  cells  certain  gran- 
ules having  substantially  the  same  chemical  and,  with  the  excep- 
tion of  their  color,  the  same  physical  properties  as  protoplasm, 
are  clearly  differentiated.      They  are  imbedded  in  the  general 
protoplasmic  mass,  and  are  not  separable  from  it  by  mechanical 
means. 

168.  Such  granules  may  be  conveniently  referred  to  three 
types,1  depending  upon  the  color :   (1)  those  which  are  green,  — 

1  Recent  investigations  render  it  probable  that  these  three  kinds  of  granules 
are  derived  from  a  common  source,  and  although  hardly  distinguishable  from 
Fio.  6.    CystoHth  from  the  upper  part  of  a  leaf  of  Ficn*  olantlca     e,  epidermis; 
y°  CC>  <7St0mi1 ;  Ch'  rh-  Cells  «™*«n»n*  elilorophvll.    It  will  he  observed 

the  cy'tolitl1  ""P"""  to  *  »tt«*«» ">  *•  '"™  *»«  of  the  upper 


CHLOROPHYLL   GRANULES. 


11 


Chloroplastids,  or  chlorophyll  granules,  also  called  chloroleu- 
cites ;  ( 2)  those  which  have  some  color  other  than  green,  — 

Chromoplastids,  or  chromoleucites  ;  (3)  those  which  are  devoid 
of  color,  —  Leucoplastids,  or  leucites. 

169.  Chlorophyll  Granules, 
or  Chloroplastids ,  are  met  with 
in  the  green  parts  of  all  plants  ; 
in  fact,  to  them  the  green  color 
is  due.      But  they  are  some- 
times masked  by  the  presence 
of  color  in  the  cell-sap.    Their 
shape  is  spherical  or  spheroidal, 
and  somewhat  flattened.    They 
have  an  average  diameter  of  2  to 
5  fj.,  but  many  granules  are  con- 
siderably larger  than  this.     It 
frequently  happens  that  they  be- 
come of  great  size,  owing  to  the 
presence  of  solid  contents, — for 
instance,  starch, — which  may 
accumulate  in  large  amount. 

170.  If  the  granules  are  sub- 
jected to  the  action  of  alcohol, 
their  coloring  matter  is  wholly 
removed  ;  but  they  retain  their 
former  volume  and  shape,  ap- 
pearing faintly  outlined  in  the 
protoplasmic    mass    in    which 
the}'  are  imbedded.     Hence  it 
is    proper    to    distinguish    be- 
tween the  chlorophyll  bod}-  of 
the  chloroplastid  and  the  chloro- 
phyll pigment  which  imparts  to  7 
it  its  characteristic  color. 

The  chlorophyll  body  may  be  shown,  by  the  process  described 
in  61,  to  be  somewhat  spongy  in  structure,  and  to  have  on  its 

each  other  at  the  outset,  become  Chloroplastids,  chromoplastids,  or  leueopla.'-- 
tids,  according  to  the  part  which  each  is  to  play.  Moreover,  one  kind  oi 
granule  can,  under  certain  conditions,  perform  work  which  properly  belongs  to 
another,  and  hence  it  is  not  always  easy  to  identify  the  different  kinds.  In 
most  cases,  however,  their  discrimination  is  very  simple. 
They  arc  also  called,  collectively,  Chromatophores. 


FIG.  7.    Chlorophyll  granules  in  tbe  leaf  of  Vallisneria  sj.iralis. 


(Weiss.) 


4'2  THE    VEGETABLE   CELL   IN    GENERAL. 

exterior  a  delicate  film.  Meyer  believes  that  the  coloring  matter 
takes  the  form  of  grains  of  extreme  minuteness  which  are  inter- 
spersed through  the  whole  substance,  while  Tschirch  holds  that 
the  pigment,  dissolved  in  a  liquid  similar  to  the  ethereal  oils,  is 
diffused  through  the  mass. 

171.  If  starch  is  present  in  large  amount  in  chloroplastids, 
iodine  causes  at  once  a  deep  bluish-brown  color  ;  but  if  the  starch 
is  not  very  abundant,  the  characteristic  blue  reaction  is  concealed 
by  the  yellow  produced  by  the  protein  reaction  of  the  protoplasm. 
Hence  it  is  well,  after  having  removed  the  chlorophyll  pigment 
by  alcohol  and  subsequent  washing  with  water,  to  treat  the  speci- 
men with  moderatel}'  strong  potassic  hydrate  in  order  to  dissolve 
the  protein  matters.  If  this  has  been  well  done,  and  the  speci- 
men carefully  freed  from  the  potash,  the  protoplasmic  mass  and 
its  imbedded  granules  will  seem  to  have  complete!}-  disappeared ; 
but  the  skilful  use  of  oblique  illumination  will  show  that  an  un- 
dissolved  trace  of  something  having  the  former  contours  remains 
behind.  Application  of  iodine  brings  out  minute  blue  j>oints 
where  the  granules  were. 

Chloral  hydrate  of  the  strength  recommended  in  53  may 
replace  potassic  hydrate  in  this  examination. 

172.  The  starch  in  chlorophyll  granules  is  sometimes  wholly 
within  the  grannie ;  but  it  is  occa- 
sionally —  especially  in  the  case  of 
flattened  granules  —  found  on  their 
exterior,  forming  a  noticeable  pro- 
tuberance. 

173.     When    a   plant    containing 
8  chlorophyll  granules  is  kept  for  a 

time  in  darkness,  the  production  of 

starch  is  arrested  ;  and  if  other  forms  of  activity  continue,  even 
that  starch  which  has  already  accumulated  in  the  granules  soon 
disappears.  Furthermore,  the 
color  of  the  granules  is  changed 
from  green  to  yellow  ;  and  if  the 
change  is  not  arrested  at  this 
point  by  bringing  the  plant 
again  into  the  light,  all  the 
granules  will  break  up  and  be- 
come apparently  merged  in  the 

^  Fron,  the  cortex  of 


LEUCOPLASTIDS. 


43 


general  protoplasmic  mass  of  the  cells,  being  no  longer  recog- 
nizable.   Those,  however,  which  have  been  changed  no  further 


than  by  loss  of  color,  closely  resemble  another  kind  of  granule ; 
namely,  leucoplastids.    (For  exceptions  see  Chapter  X). 

174*    Leucoplastids.    These  are   found   in   parts   which   are 
normally  devoid  of  chlorophyll,  such  as  tubers,  rhizomes,  etc. 


They  may  be  wholly  colorless,  or  faintly  tinged  with  yellow,  and 
hence  are  apt  to  escape  detection.  They  may  be  considered  as 
the  points  around  which  starch  accumulates  when  stored  for  the 
future  needs  of  the  plant.  Schimper,1  who  first  accurately  de- 
scribed them  in  all  their  relations,  terms  them  "starch  genera- 
tors ; "  they  are  also  known  as  amylogenic  bodies,  which  of 
course  means  the  same  thing.  They  are  seen  to  the  best  advan- 

1  Schimper:  Bot.  Zeit.,  1880,  1881,  1883. 

FIG.  9  b.  Same,  more  advanced:  a,  the  amylogenic  bodies  are  covered  with  starch- 
grains;  b,  two  nuclei  on  a  cell-wall,  each  surrounded  by  amylogenic  bodies  covered  by 
starch.  8{».  (Schimper.) 

Fio.  10.  a.  Young  amylogenic  bodies  surrounding  the  nucleus  of  a  cell  in  the  root  of 
Phajusgrandifolius;  6,  same,  with  starch-grains  developing;  c,  same,  more  advanced. 
•f0.  (Schimper.  | 


44  THE    VEGETAIU.E   CELL    IN   GENERAL. 

tage  in  thin  sections  of  many  starchy  tissues,  by  the  use  of  dilute 
tincture  of  iodine,  which  colors  them  more  or  less  deeply  yellow. 
Millon's  reagent  colors  them  red. 

Owing  to  the  minuteness  of  the  leucoplastids,  the  following 
explicit  directions  by  Strasburger  will  aid  in  their  detection : 
Make  thin  longitudinal  sections  through  the  upper  part  of  a 
young  pseudobulb  of  Phajus  grandifolius,  taking  care  that  the 
cut  extends  to  its  green  surface.  Immediately  place  the  sections 
in  an  alcoholic  solution  of  iodine  diluted  with  one  half  its  volume 
of  water.  (Picric  acid  may  be  advantageously  used  instead  of 
the  iodine  solution.)  In  good  preparations  the  leucoplastids  will 
be  seen  in  the  inner  part  of  the  section  as  small  staff-shaped 
bodies  which,  at  the  first  glance,  appear  to  be  homogeneous,  but 
are  afterwards  recognized  as  somewhat  granular  in  structure. 
The  section  is  next  to  be  examined  nearer  its  outer  part,  and  it 
will  then  be  seen  that  the  bodies  there  possess  a  green  color, 
are  larger,  and  lenticular  in  form.  They  are  also  plainly  porous, 
their  increase  in  size  being  apparently  associated  with  a  spongi- 
ness  of  their  substance.  Their  size  diminishes  towards  the  outer 
cellular  layers,  they  become  somewhat  rounded,  and  finally  take 
the  familiar  form  of  chlorophyll  granules.  Prismatic  colorless 
protein  crystals  are  frequently  associated  with  these  bodies. 
In  sections  which  are  placed  in  water,  the  leucoplastids  disap- 
pear almost  instantaneously,  and  even  the  chlorophyll  granules 
soon  begin  to  disorganize,  while  the  swollen  protein  crystals  then 
appear  as  colorless  parts  of  the  latter. 

In  the  rhizome  of  Iris  Germanica  the  sections  for  examination 
must  be  taken  parallel  to  the  surface.  In  uninjured  cells  the 
leucoplastids  appear  as  collections  of  protoplasm  at  the  end  of 
each  starch-granule.  If  the  section  is  in  water,  the  leucoplastids 
become  granular  and  finally  break  up  into  minute  granules  which 
show  the  Brownian  or  molecular  movement.1 

Chromoplastids .  or  the  color-granules  which  occur  abundantly 
in  flowers  and  fruits,  will  be  specially  treated  later. 

175.  Protein  granules.  The  protein  matters  in  plants  have 
been  divided  into  two  classes:  (1)  the  active,  such  as  active 
protoplasm,  the  nucleus,  etc. ;  (2)  the  reserve,  which  can  change 
their  dormant  condition  and  become  active  when  occasion  de- 
mands. Inactive,  amorphous  protoplasm,  as  it  sometimes  exists 
in  certain  cells,  where  it  is  simply  a  tough  shapeless  mass,  does 
not  need  furtluer  consideration  at  present ;  the  reserve  matters 

1  Strasburger:  Da*  botan.  Practicuin,  1884,  j)j>.  67,  68- 


PROTEIN    GRANULES. 


45 


now  to  be  examined  being  those  which  take  the  form  of  more  or 
less  regular  grains.     These  which  are  known  as 

176.  Protein  granules  may  be  either  independent,  or  asso- 
ciated with  other  substances.  In 
nearly  all  cases  the}-  are  more  or 
less  soluble  in  water,  and  hence 
require  special  treatment  for  their 
satisfactory  examination.  Cells 
supposed  to  contain  them  may  be 
placed  for  examination  in  any  fixed 
oil,  and  the  granules  will  remain 
unchanged.  A  more  practicable 
method  of  treatment  is  suggested 
by  Pfefler ;  namely,  to  subject  the 
granules  to  the  action  of  an  alco- 
holic solution  of  mercuric  chloride, 
by  which  they  are  rendered  insoluble  (see  63).  The  solution 
is  made  by  dissolving  one  part  of  mercuric  chloride  (corrosive 
sublimate)  in  fifty  parts  of  absolute  alcohol ;  in  this  solution 
the  thin  sections  of  seeds,  etc.,  suspected  of  containing  pro- 
tein granules,  must  be  kept  for  at  least  twelve  hours.  Upon 
removal  to  water,  after  this  period,  they  remain  substantially 
unchanged.  The  precaution  must  be  taken  not  to  touch  with 
any  metal  the  sections  after  they  have  been  placed  in  the 

mercuric  chloride  solution. 
The}'  must  be  removed  by  a 
camel's-hair  brush. 

177.  The  protein  matter 
of  which  protein  granules 
consist  may  be  wholly  with- 
out definite  shape,  or  a  por- 
tion may  assume  somewhat 
the  form  of  crystals.  The 
latter  have  been  called  pro- 
tein crystals  or  crystalloids,  and  they  are  generally  associated, 
in  the  granules  of  which  they  form  a  part,  with  inorganic  matters 
either  amorphous  or  crystalline.  Hence  in  some  protein  gran- 
ules we  have  to  distinguish  between  the  inorganic  contents,  the 

FIG.  11.  Cells  from  cotyledons  of  Vlcia  sativa,  showing  protein  matters  in  a  finely 
divided  state,  intermingled  with  starcli-granules.  (Schmidt.) 

FK;.  12.  Protein  granules  from  the  endosperm  of  Ricinus  communis.  The  specimen 
is  in  oil.  *?°.  (Pfetter  ) 

FK;  13.  Protein  grannies  from  the  endosperm  of  Ricinns  commnnis.  The  specimen, 
first  treated  with  mercuric  chloride  in  absolute  alcohol,  is  now  in  water.  <?°.  (Pfefter.) 


46 


THE   VEGETABLE   CELL    IN    GENERAL. 


protein  crystal-like  bodies,  and  the  protein  basis  or  stroma  in 
which  all  of  these  are  held. 

The  protein  basis  sometimes,  if  not  alwa3-s,  appears  to  consist 
of  two  substances,  differing  in  their  solubility  in  water,  and  com- 
mingled as  granulose  and 
cellulose    are    in    starch- 
granules.     While  the  pro- 
tein basis  is  generally  very 
c  soluble  in  water  (not  per 

se,  but  owing  to  the  pres- 
ence of  potassic  phos- 
phate), the  protein  crystals  are  insoluble,  or  only  slightly  affected 
by  it,  usuall}'  becoming  more  or  less  swollen.  After  solution  of 
the  protein  basis  has  taken  place,  a  delicate  membrane  is  left 
behind,  and  through  this  transparent  film  the  protein  crystals 
are  clearly  seen.  The  relative  amounts  of  protein  basis  and 
protein  crystals  vary  widehy  ;  in  some  cases  the  former  appears 
to  be  wanting,  the  latter  wholly  filling  the  interior  of  the  mem- 
brane. Such  crystals  appear  in  potato-tubers  in  the  form  of 


small  cubes.  Protein  crystals  of  great  beauty  are  easily  dem- 
onstrated in  the  endosperm  of  the  common  Brazil-nut  (Ber- 
tholletia).  Very  instructive  phenomena  are  presented  when 
different  sections  of  the  seed  are  subjected  to  the  following 
reagents;  (1)  osmic  acid  (one  per  cent  solution) ;  (2)  hteniatoxylin 


FIG.  14.  Single  protein  granules  treated  as  In  Fig.  12.    »?".    (Pfeffer.) 

FIG.  15.  Protein  granules  from  Silybtim  marlanum.  In  the  cell  on  the  left  they  have 
crystalline  contents;  In  that  on  the  right,  globolds.  This  section  was  taken  from  the 
cotyledons  of  a  dormant  seed,  and  after  treatment  with  mercuric  chloride  in  alcohol  was 
placed  in  water.  »p>.  (Pfeffer.) 

FIG.  16.  The  mesh  of  the  ground  mass  of  the  cell  has  been  cleared  by  dilute  potassic 
hydrate  and  hydrochloric  m-id.  n  =  nucleus.  •?•».  (Pfeffer.) 

FIG  17.  Cells  from  the  cotyledons  of  a  germinating  seed  which  has  just  ruptured  the 
seed-coat.  The  protein  granules  have  disappeared,  but  their  contents  are  recognizable. 
•?".  (Pfeffer.) 

FIG  18.  Stlybum  marlanum  Cell  from  the  cotyledon  of  a  nearly  ripe  seed  In  which 
the  formation  of  protein  granules  has  just  begun.  »','".  (Pfeffer.) 


STAECH.  47 

in  concentrated  glycerin;  (3)  concentrated  potassic  hydrate, 
water  being  added  afterwards.  Permanent  preparations  of  pro- 
tein crystals  can  be  made  by  first  acting  on  the  section  with 
mercuric  chloride  for  a  day  or  more,  washing  in  water,  staining 
with  eosin,  and  finally  mounting  in  potassic  acetate  (101). 

The  inorganic  matters  associated  with  the  protein  crystals 
in  protein  grannies  are  either 
(1)  amorphous  or  globular  con- 
cretions of  a  double  phosphate  of 
calcium  and  magnesium,  known 
as  yloboids,  or  (2)  crystalline 
clusters  of  calcic  oxalate. 

The   protein   granules,   espe- 
cially those  which  are  most  com- 
plex in  their  composition,  are  also  known  as  Aleurone  grains. 
The  protein  crystals  are  general!}-  termed  crystalloids.1     For  an 
analytical  classification  of  protein  granules  in  seeds,  see  pages 
182  and  183. 

178.  Starch,  the  principal  form  in  which  the  elaborated  food 
of  plants  is  held  in  reserve,  occurs  as  minute  spheroidal  or 
polyhedral  granules.  Under  a  suf- 
ficiently high  power,  and  with 
proper  management  of  the  mirror 
of  the  microscope,  tho  single  gran- 
ules exhibit  an  appearance  of 
stratification  which  is  sometimes 
very  distinct,  but  more  commonly 
obscure  ;  in  the  latter  case  dilute 
chromic  acid  can  be  used  to  ren- 
der the  stratification  plainer.  The 
layers  of  stratification  are  ar- 
ranged around  a  point,  —  often  very  eccentrically,  as  in  potato 

1  The  fact  that  protein  crystals  have,  as  a  rule,  less  constancy  in  their  angles 
than  inorganic  crystals,  taken  together  with  the  fact  of  their  swelling  when 
immersed  in  water,  has  led  authors  to  speak  of  them  as  crystalloids  rather  than 
as  crystals.  But  Famintzin  has  recently  shown  that  certain  crystalline  forms 
artificially  produced  obscure  these  distinctions,  since  they  agree  more  closely  in 
some  of  their  physical  characters  with  organic  structures  than  with  ordinary 
inorganic  crystals  (Ber.  der  deutsch.  hot.  Gesellsch.,  1884,  p.  32). 

FIG.  19.  A  cell  from  nutmeg  lying  In  oil.  In  the  ground  mass  are  very  numerous 
crystals  of  fat.  Some  of  the  granules  are  compound  starch-granules,  but  others  are 
protein  granules  with  crystalloids.  The  rhombic  granule  has  hardly  any  envelope. 
*f>.  (Pfeffer.) 

FIG.  20.  Globoids  of  Vitis  vinifera.    «?"•    (Pfeffer  ) 

FIG.  21.  Large  protein  granules  from  Vitis  vinifera.    '?".    (Pfeffer.) 

FIG.  22   Wheat-grain,  showing  cells  containing  starch-granules.    (Schmidt ) 


48 


THE  VEGETABLE   CELL   IN   GENERAL. 


0 


starch,  or  with  great  regular- 
ity, as  in  wheat.  This  point  is 
known  as  the  nucleus,  or  hilum. 
If  two  or  more  nuclei  are  dis- 
cernible, the  granule  is  said  to 
be  compound. 
23  Occasionally  many  small  sin- 

gle granules  cohere  slightly  to 

form  an  aggregate  which  can  be  easily  broken.     According  to 
Wiesner,  there  ma}*  be  as  many 
as  30,000  granules  in  a  single 
aggregate  of  this  kind. 

Both  simple  and  compound 
grannies  ma}-  occur  in  the  same 
cell,  but  some  plants  have  only 
simple,  and  others  only  com- 
pound granules.  Canna  and 
Curcuma  may  be  cited  as  exam- 
ples of  the  former ;  Jatropha,  of 
the  latter. 

Since  starch  occurs  in  every 
plant  in  all  stages  of  development,  the  size  of  the  granules  must 
be    extremely    variable.      Nevertheless,    a 
statement  of  the  more  common  limits  may 
aid  in  their  identification. 

Wiesner  gives  the  following  limits  of  size 
for  some  of  the  more  common  sorts  of  starch, 
first  grouping  them  into  small,  medium,  and 
large  grannies. 

Small  granules  (from  0.002  to  0.015  mm.)  : 
as  the  simple  granules  of  rice,  oats,  buck- 
wheat ;  also  the  smaller  granules  of  wheat,  rye,  barley,  etc. 

Medium  granules  (from  0.02  to  0.0f>  mm.)  :  as  the  compound 
granules  of  rioc  and  oats,  the  larger  ones  of  wheat,  rye,  and 
barley,  the  simple  granules  of  Indian  corn,  and  of  the  common 
leguminous  plants. 

Large  granules  (distinguishable  ns  granules  to  the  naked  eye)  : 
as  the  simple  granules  of  Curcuma  leucorrhiza,  Canna  edulis, 
potato,  etc. 


Fto.  23  Starch-granules  from  the  bulb  of  Phajns  grandffollns,  showing  the  nu- 
cleus at  the  upper  part  and  the  starch  generator  or  amylogenic  body  below.  •}•. 
(Sclilinper. ) 

Fio.  24.  Cells  from  potato-tuber,  showing  starch-granule*     (Schmidt.) 
Fm.  25.  Starch-granules  from  sarsaparilla.    (Berg  and  Schmidt.) 


STARCH. 


49 


Starch   is   insoluble  in   cold  water,  but  forms  with   boiling 
water  a  paste  in  which  all  traces  of  structure  are  lost.     If  a 


specimen  of  starch  be  gently  heated  with  water  upon  a  glass 
slide,  the  granules  will  be  seen  to  swell  at  a  temperature  of 


40°-f>0°  C.,  and  the  appearance  of  stratification  will  often  be- 
come plainer.    The  alkalies  and  mineral  acids  generally  hasten  the 

FIG.  26.    Starch-granules  of  wheat.  FIG.  29.    Starch-granules  of  oats. 

•    Fio.  27.    Starch-granules  of  Indian  corn.     FIG.  30.    Starch-granules  of  rice. 

FIG .28.    Starch-granules  of  barley.  Fio.  31.    Starch-granules  of  potato. 

FIG.  32      Starch-granules  of  Maranta  (arrow-root) 

FIG.  33.    Starch-granules  of  Boroaria  I'Chilt  arrow-root). 

Fio  34     Starch-granules  of  Vicla  sativa,  var.  leucosperma.     All  the  figures  of 
starch  are  from  Berg  and  Schmidt. 

4 


50  THE   VEGETABLE   CELL   IN   GENERAL. 

formation  of  starch-paste,  and  bring  about  some  other  changes, 
such  as  its  conversion  into  soluble  matters. 

179.  Starch  is  usually  said  to  have  the  following  composition, 
C6H10O3,  and  these  proportions  are  doubtless  correctly  stated  ; 
but  it  is  probable  that  the  molecular  constitution  is  more  com- 
plex than  this  formula  would  indicate.1 

180.  When  starch  is  acted  on  by  saliva  or  pepsin,  it  is  slowly 
separated  into  two  substances,  one  of  which  passes  into  solution, 
while  the  other  remains  as  a  skeleton,  and  with  little  change  of 
form.     This  delicate  framework,  which  remains  after  the  soluble 
matter  is  removed,  is  closely  related  to  cellulose,  as  shown  by 
its  behavior  with  reagents,  and  has  received  the  name  of  starch 
cellulose.   The  substance  which  is  removed  by  the  action  of  saliva 
is  termed  granulose. 

181.  When  starch  is  not  associated  with  too  large  a  propor- 
tion of  protein  matters,  it  can  always  be  detected  by  the  blue 
color  which  it  takes  with  iodine  in  solution  ;  but  if  protein  sub- 
stances are  present  in  considerable  amount,  the}'  ma}*  obscure 
the  reaction  b}'  the  yellowish  or  brown  color  which  iodine  im- 
parts to  them.    Iodine  does  not,  however,  always  produce  n  blue 
color  with  starch  ;  the  shade  may  vary  towards  red,  forming  a 
purple  which  ma)-  be  almost  black.     Furthermore,  as  the  tran- 
sient color  given   03-  this  reagent  fades,  it   may  pass  through 
various  tints  of  orange  and  yellow. 

Protein  matters  which  mask  the  starch  reaction  ma}-  be  re- 
moved by  careful  treatment  of  the  specimen  with  potassic  hy- 
drate (not  too  concentrated),  and  subsequent  washing  with  pure 
water.  After  such  treatment  it  sometimes  happens  that  the 
starch  appears  as  a  diffused  mass  instead  of  in  minute  dots. 

182.  When  starch-granules  are  seen  in  polarized  light  they 
generall}-  exhibit  two  crossed  lines  which  appear  to  turn  as  the 
Nicol  prism  is  revolved.     Many'  kinds  of  starch  give  under  the 
polarizer  characteristic  figures,  many  of  them  of  great  beauty. 

183.  Iniilin.  although  occurring  in  solution  in  cells,  is  never- 
theless thrown  down  in  characteristic  forms  by  means  of  the 
preservative  media  alcohol  and  glycerin,  and  can  be  examined  as 
a  solid.     If  the  root  of  Dahlia.  Helianthus,  or  any  of  the  com- 
mon Composite  which  store  up  their  food  in  fleshy  underground 
parts,  be  subjected  to  the  action  of  alcohol  for  a  few  days,  thin 
sections  will  exhibit  in  the  cells  peculiar  masses  of  a  spheroidal 


1  W.  Nageli,  however,  gives  the  formula  for  starch  as  follows 
Beitr.  z.  naheren  Kenntniss  der  Starkegrappe,  1874. 


INULIN. 


51 


form  which  are  distinct!}*  radiating  in  structure.  Occasionally 
these  masses  have  large  rifts  which  run  across  the  surface  of  the 
sphere. 

In  composition,  inulin  closely  resembles  starch,  but  does  not 
give  any  color  with  iodine.  To  de- 
tect it  when  in  solution,  a  thin  sec- 
tion of  the  plant  containing  it  is 
moistened  on  the  glass  slide  with 
absolute  alcohol,  when  a  cloudy  pre- 
cipitate will  at  once  appear ;  in  a 
short  time  (the  supply  of  alcohol 
having  been  replenished  as  it  evap- 
orates) the  specimen  grows  clearer, 
and  small  sphserocrystals  of  inulin 
are  seen.  If  now  the  specimen  is 
carefully  washed  with  water,  the 
smaller  granules  disappear  and  the 
well-defined  remain. 

184.  The  carbohydrates  dissolyed 
in  the  cell-sap  may  be  grouped  in  two 
classes  :  (1)  those  which  are  isomers 
of  cellulose  (i.  e.,  have  the  same  per- 
centage composition,  C6H10O5) ,  and  (2)  the  sugars. 

1.  The  isomers  of  cellulose  are  mucilage,  gums,  and  dextrin, 
all  of  which  are  probably  derivatives  of  starch.  Various  sub- 
stances intermediate  between  them  have  been  described,  but  the 
above  are  all  that  need  now  be  taken  into  account,  (a)  Mucilage, 
when  not  plainly  resulting  from  the  breaking  up  of  the  cell- 
wall,  is  colored  red  by  rosolic  acid,  and  the  color  is  not  readily 
removed  by  alcohol,  (b)  Tlie  gums,  of  which  cherry  gum 
may  be  taken  as  an  example,  are  not  tinged  by  rosolic  acid, 
(c)  Dextrin  can  be  detected  by  Trommer's  test,  which  Sachs  ap- 
plies as  follows  :  a  section  which  is  at  least  a  few  cells  in  thick- 
ness is  placed  in  a  porcelain  capsule  with  a  strong  solution  of 
cupric  sulphate,  and  the  liquid  is  heated  to  boiling  ;  the  specimen 
is  then  washed  in  water,  and  dipped  at  once  in  hot  potassa. 
If  the  cells  contain  either  dextrin  or  grape-sugar,  there  will 
immediately  appear  a  reddish  precipitate.  To  discriminate  be- 
tween dextrin  and  grape-sugar,  it  is  merely  necessary  to  keep 
portions  of  the  plant  to  be  examined  in  90  or  95  per  cent  alcohol, 
which  will  dissolve  out  the  sugar  and  leave  the  dextrin,  if  any 


FIG.  35.    Spliaerocrystala  of  inulin  from  root  of  Cicbory  treated  with  alcohol    »f«. 
(Jacobs. )  .  • 


52  THE   VEGETABLE  CELL   IN   GENEKAL. 

is  present.  Usually  all  the  grape-sugar  is  extracted  in  a  day 
or  two. 

2.  The  sugars.  Grape-sugar  has  been  just  referred  to  as 
giving  the  same  reaction  as  dextrin  with  Trommer's  test.  Its 
formula  is  C0H12OC.  Cane-sugar,  which  has  the  formula  C^H^On, 
gives  no  red  precipitate  with  the  same  test,  but  the  liquid  in  the 
cells  becomes  bright  blue,  and  quickly  diffuses  into  the  potassa.1 

185.  Crystals  are  of  such  general  occurrence  in  widely  differ- 
ent orders  of  the  higher  plants,  that  there  are  perhaps  none 
in  which  they  may  not  be  detected.  They  have  been  found  in 
nearly  all  parts  of  the  vegetable  structure,  more  commonly  in 
the  interior  of  parenchyma  cells,  sometimes  in  specialized  crys- 
tal-receptacles, occasionall}'  in  the  very  substance  of  the  cell- 
wall.  The}'  occur  either  singly  or  in  groups  ;  either  separate  or 
barely  coherent,  or  in  various  degrees  of  combination. 

When  solitary  and  simple  the}'  are  usuall}-  octahedra  or 
prisms,  and  their  aggregations  are  combinations  of  these.  Good 
octahedral  crystals  are  afforded  by  the  petioles  of  Begonia; 
examples  of  the  prismatic  form  are  found  in  the  outer  scales  of 
onions,  in  orange  leaves,  in  the  inner  bark  of  maples  and  apple- 
trees,  and  in  most  of  the  tissues  of  Iris  and  its  allies. 

When  the  prisms  are  very  long  and  slender  their  angles  and 
faces  are  seldom  well  defined.2  Indeed,  the  most  attenuated 
forms  are  usually  terete,  or  slightly  flattened,  and  taper  gradually 
to  a  point  at  botli  ends.  To  these  De  Candolle  long  ago  gave 
the  name  Raphides,  —  that  is,  needles.8  These  are  generally 
massed  in  a  compact  bundle,  like  a  wheat-sheaf,  occupying  a 
large  part  of  the  interior  of  the  containing  cell. 

Raphides  are  by  no  means  of  such  general  occurrence  as 
are  ordinary  c^-stals,  but  (as  Gulliver  has  pointed  out)  are 
seemingly  restricted  to  certain  orders.4  They  are  universal  in 
Araceaj  and  Onagracese.  In  the  common  Arums  and  Callas, 
raphides-bearing  cells  may  readily  be  found  in  the  parenchyma 


1  Pringsheim's  Jahrb.,  iii.  p.  187.     In  the  Sitzungsber.  d.  k.  Akad.  Wien, 
for  1 859,  Sachs  has  given  colored  figures  illustrative  of  these  reactions. 

2  When  the  longer  prisms  are  clearly  denned,  they  are  referable  to  the  mono- 
clinic  system.     Measurements  of  angles  are  given  by  Holzner,  in  Flora,  1864, 
p.  292.     A  paper  by  Bailey  (Am.  Journ.  of  Sc.  and  Arts,  vol.  xlviii.,  1845, 
p.  17)  also  contains  determinations. 

*  Organographie,  1827,  p.  125. 

*  Gulliver  has  examined  representative  plants  of  all  the  more  inijwrtant 
orders  of  the  British  Flora,  with  respect  to  the  occurrence  of  diagnostic  crys- 
tals (Annals  and  Magazine  of  Natural  History,  1863  to  1867). 


CRYSTALS. 


53 


<>f  the  leaves,  and  detached  entire ;  on  becoming  turgid  when 
wetted,  they  will  usually  discharge  their  raphides  one  by  one 
from  one  or  both  ends  of  the  cell  until  the  bundle  is  almost 
exhausted.1 

186.  When   the  ordinary  octahedral   or    prismatic   crystals 
are  aggregated  or 

combined,  they 
generally  compose 
a  spherical  mass. 
Such  aggrega- 
tions are  of  two 
principal  types  : 
( 1 )  those  made 
up  of  many  small 
crystals  irregular- 
ly grouped,  and 
usually  presenting 
sharp  points  over 
the  surface,  as  36  A 

in  Fig.  36 a;  (2) 

those  with  a  distinctly  radiated  structure  (Fig.  36 »).  Good 
examples  of  the  former  are  abundant  in  the  foliage  of  Chenopo- 
diaceae  and  the  stems  of  Cactacete.  Clusters  belonging  to  the 
latter,  or  stellate,  type  are  not  uncommon  in  Malvaceae.  Both 
forms  have  been  termed  Sphcer  aphides*  and  Sphere-crystals. 
The  term  cystolith,  sometimes  improperly  applied  to  them, 
should  be  wholly  restricted  to  the  peculiar  bodies  described  on 
page  40. 

187.  Owing  to  the  mechanical  difficulty  of  isolating  plant- 


1  Turpin  (Annales  des  Sc.  nat.,  ser.  2,  tome  v.,  1836)  described  the  raphides- 
bearing  cells  of  Caladium,  in  which  this  discharge  takes  place,  under  the  name 
of  biforines. 

2  "  They  are  most  irregularly  scattered  through  the  tissues  of  the  plant. 
...  I  have  never  failed  to  find  them  in  a  single  species  of  the  order  Caryo- 
phyllaceae,  Geraniaceae,  Lythracese,  Saxifragacea,  and  TJrticacese,  and  believe 
that  few  if  any  orders  could  be  named  in  which  sphseraphides  do  not  exist  as 
part  and  parcel  of  the  healthy  and  growing  structure  of  the  plant  "  (Gulliver, 
in  Annals  and  Magazine  of  Natural  History,  vol.  xii.,  1863,  p.  227). 

FIG.  36.  The  more  Important  forms  of  crystals  of  calcic  oxalate :  a,  three  cells  from 
the  petiole  of  Begonia  manicata ;  b,  from  the  leaf  of  Tradescantia  discolor ;  c  and 
d,  from  the  leaf  of  Allium  Cepa;  e,  from  the  inner  bark  of  .Ksriilus  Hippocastanum ; 
/,  from  the  leaf  of  Cycas  revoluta ;  </,  a  cell  containing  raphides,  from  the  frond  of 
Lemna  trisulca;  h,  a  single  crystal  from  the  same,  more  highly  magnified;  i,  sphaero- 
crystal  from  Phallus  eaninus.  (Kny. ; 


54        THE  VEGETABLE  CELL  IN  GENERAL. 

crystals  for  examination,  their  chemical  composition  has  not  yet 
been  determined  with  certainty  in  all  cases.  That  a  protoplas- 
mic film  usually  envelops  both  solitary  and  aggregated  crystals, 
can  be  shown  by  the  method  pointed  out  by  Payen  ; '  namely, 
by  dissolving  the  crystal  slowly  in  very  dilute  nitric  acid,  and 
testing  with  iodine,  when  the  film  will  become  yellowish-brown. 
It  has  also  been  made  out  be}'ond  question  that  some  crystals 
have  a  considerable  admixture  of  cellulosic  matter,  and  that  a 
few  others  are  covered  b}'  a  membrane  of  cellulose.2  But  these 
two  substances  do  not  obscure  the  chemical  reactions  in  ordinary 
cases,  by  which  it  has  been  shown  that  the  larger  number  of  crys- 
tals consist  of  calcic  oxalate,  after  which,  in  frequency  of  occur- 
rence, comes  the  carbonate  of  the  same  metal.  These  two  salts 
can  be  easily  distinguished  from  each  other  by  the  following 
simple  tests :  — 


Reagent, 

Calcic  Oxalate. 

Calcic  Carbonate. 

Acetic  acid. 
Hydrochloric  acid. 

No  effect 

Dissolves  without  ef- 
fervescence. 

Dissolves  with  effer- 
vescence. 
Dissolves  with  effer- 
vescence. 

Since  these  two  salts  may  occur  in  the  same  specimen,  it  is  best 
to  use  acetic  acid  first ;  by  this  agent  all  traces  of  the  carbonate 
are  removed,  and  hydrochloric  acid  can  then  be  applied  in  order 
to  detect  the  presence  of  oxalates.  Sanio8  and  Holzner  have 
shown  conclusively  that  man}'  crystals  which  have  been  supposed 
to  be  calcic  carbonate  consist  merely  of  the  oxalate. 

Crystals  of  calcic  sulphate  have  been  reported  as  occurring 
in  certain  Musaceae,4  in  the  bark  of  the  willow,  in  the  roots  of 
aconite,  bryony,  and  rhubarb ;  and  also  in  the  root  of  a  young 
bean.8  Calcic  phosphate  is  said  to  have  been  detected  in  the 

1  Payen  :  Mem.  des  savants  Grangers,  ix.,  1846,  p.  91. 

2  Rosanoff  (Bot.  Zeit.,  1865,  1867),  Crystals  in  pith  of  Ricinus  and  Kerria. 
Pfitzer  (Flora,  1872),  crystals  in  the  leaves  of  orange  and  the  bark  of  many 
trees. 

Hilgers  has  investigated  the  occurrence  of  crystals  at  different  periods  of 
growth  of  different  organs.  From  his  results  it  appears,  (1)  that  in  the  very 
youngest  parts  no  crystals  are  to  be  fonnd  ;  (2)  they  appear,  however,  very 
early  in  most  parts,  and  (3)  speedily  attain  their  maximum  size,  after  which 
they  undergo  no  change  (Pringsheim's  Jahrb.,  vi.,  1867,  p.  285). 

«  Sanio  :  Monatsber.  Berliner  Akad.,  1857. 

4  Van  Tieghem  :  Trait£  de  Botnnique,  p.  526. 

8  Sitzungsberichte  der  Wiener  Akad.,  xxxvii.,  1859,  p.  106. 


CBYSTALS.  55 

wood  of  Tectona  grandis  (Indian  Teak).1  HoLzner2  uses  the 
following  reaction  to  detect  calcic  sulphate  :  a  solution  of  baric 
chloride  (not  too  concentrated)  is  brought  into  contact  with 
the  cr}-stal  under  examination ;  calcic  sulphate  soon  becomes 
covered  with  a  whitish  deposit  of  baric  sulphate.  This  test 
failed  to  show  the  presence  of  calcic  sulphate  in  the  plant- 
crystals  hitherto  referred  to  this  salt ;  they  all  gave,  however, 
the  reaction  for  the  oxalate. 

188.  Crystals  closely  resembling  in  most  respects  those  which 
are  found  in  cells  can  be  produced  by  Vesque's  method.8    Three 
test-tubes  are  placed  side  by  side :  in  the  first  is  a  moderately 
strong  solution  of  calcic  chloride  ;  in  the  middle  one,  a  five  per 
cent  solution  of  sugar ;  and  in  the  third,  a  solution  of  potassic 
oxalate.     From  the  liquid  in  the  first  to  that  in  the  second  a 
short  strip  of  filtering-paper  runs,  and  a  similar  strip  passes 
from  the  second  to  the  third  test-tube ;  and  thus  the  liquids  in 
the  three  tubes  are  brought  into  indirect  contact.     Ciystals  will 
be  formed  in  the  middle  tube,  their  character  depending  upon 
the  nature  of  the  liquid  there.     In  a  solution  of  sugar,  raphides 
are  produced ;    in  pure  water,  prisms  of  small  size,  but  with 
sharply  defined  faces  and  angles. 

189.  According  to  Souchay  and  Lenssen,4  raonoclinic  ("  Clino- 
rhombic")  crystals  of  calcic  oxalate  containing  two  equivalents 
of  water  are  produced  upon  quick  precipitation,  while  by  ver}- 
slow  action  right  octahedra  with  six  equivalents  of  water  are 
formed. 

A  few  works  of  reference  are  the  following :  — 

MOHL.  Principles  of  the  Anatomy  and  Physiology  of  the  Vegetable  Cell. 
Translated  by  Heufrey  (London,  1852).  An  octavo  of  158  pages.  This  is  an 
excellent  translation  of  a  classical  work. 

HOFMEISTER.  Die  Lehre  von  der  Pflanzenzelle  (Leipzig,  1867).  An  octavo 
of  397  pages.  The  volume  treats  very  fully  of  the  physical  properties  of  pro- 
toplasm. 

EBEHMAYER.  Physiologische  Chemie  der  Pflanzen  (Berlin,  1882).  This  is 
the  first  volume  of  an  expensive  work  which  deals  with  the  relations  of  plants 
to  soil  and  climate. 

HUSEMANX  und  HILGER.  Die  Pflanzenstoffe  (Berlin,  1882).  Two  large 
volumes.  It  has  very  extensive  references  to  the  literature  of  the  subject,  and 
most  of  its  abstracts  are  excellent. 

1  Pies:    Naturkundig  Tijdschrift  voor  Nedrlandsch-Indie,    1858,   p.   345. 
Quoted  from  Holzner. 

2  Flora,  1864,  p.  283.     This  communication  contains  a  good  abstract  of  the 
literature  of  plant-crystals  up  to  1862. 

8  Ann.  des  Sc.  nat.,  ser.  5,  tome  xix.,  1874,  p.  300. 
4  Annalen  der  Chemie  und  Pharmacie,  c.,  1856,  p.  311. 


CHAPTER  II. 

CELLS    IN   THEIR    MODIFICATIONS    AND    KINDS,    AND    THE 
TISSUES   THEY   COMPOSE. 

190.  WHILE  cryptogamous  plants  of  the  lower  grade  may 
consist  of  single  cells,  or  of  a  series  or  stratum  of  simple  and 
undifferentiated   cells,   phaenogamous   plants,    although    equally 
simple   and    homogeneous  at  the  initiation  of  each  individual, 
develop  into  a  more  complex  organization,  at  an  early  period 
differentiate  some  of  their  cells  into  peculiar  kinds,  multiply  the 
kinds  into  tissues  or  fabric,  and  of  these  build  up  the  organs 
and  parts  which  are  familiar  in  ordinary  vegetation. 

191.  The  microscropical  study  of  the  parts  even  of  a  single 
herb  or  tree,  and  much  more  that  of  a  variety  of  plants,  reveals 
numerous  forms  or  kinds  of  cells,  and  also  (as  might  be  expected 
from  their  common  origin)  brings  to  view  series  of  gradations 
between  the  kinds,  sometimes  even  between  those  which  are, 
upon  the  whole,  widcry  differentiated  from  each  other.     While, 
therefore,  a  general  classification  of  the  cells  of  an}-  ordinary 
plant  into  kinds  is  easy,   any  classification  which   shall   satis- 
factorily exhibit  our  present  knowledge  of  the  histological  ele- 
ments, and  discriminate  their  varieties,  is  very  difficult,  if  not 
at  this  time  practically  impossible.    At  least,  it  must  be  said  that 
the    most  recent  classifications  are  based    upon    considerations 
of  a  character  too  recondite  and  special  to  be  mastered  at  the 
beginning  by  an  ordinan-  student. 

192.  The  most  general  and  obvious  division  of  the  histological 
components  of  a  stem,  root,  or  leaf  would  be  into,  (1)  funda- 
mental or  typical  cells,  and  (2)  transformed  cells.     The  first  are 
those  in  which  the  normal  cellular  character  persists  without  pro- 
found, if  any,  alteration  or  disguise  ;  as  in  the  pulp  of  leaves,  the 
pith  of  stems,  and  in  a  portion  of  the  bark.    The  second  are  those 
which  assume  or  affect  lengthened  or  fibrous  forms  and  a  longi- 
tudinal development  (at  least  in  all  axes,  and  commonly  in  leaves 
and  other  expanded  organs),  and,  combined  into  threads,  fasci- 
cles, bundles,  or  more  massive  structures,  constitute  the  frame- 
work, which  imparts  solidity  and  strength  throughout.      Some 


TYPICAL   CELLS.  57 

of  these  cells  are  so  long  in  proportion  to  their  breadth,  and  of 
such  diminished  calibre,  that  the}1  have  naturally  been  called 
fibres,  although  all  gradations  between  them  and  typical  cells 
ma}'  be  demonstrated.  All  these  cells  are  interchangeably 
called  woody  fibres  or  wood-cells,  and  one  kind  of  them  takes 
the  name  of  bast-cells. 

193.  Others  are  of  larger  calibre,  are  peculiarly  marked  by 
thickenings  on  certain  lines  or  in  certain  patterns,  incline  to  be 
developed  end  to  end  in  a  chain  or  row,  and  to  become  confluent 
at  the  junctions,  so  as  to  form  conduits  of  considerable  length  ; 
these    are   called   vessels,    or    ducts.      Vessels  and    fibres  are 
associated  in  the  plant ;  almost  every  separate  thread  of  frame- 
work consists  of  both,  and  so  is  called  a  fibro-vascular  bundle  or 
fascicle.     Moreover,  the  known  gradations  between  the  two  are 
such  as  to  render  a  complete  distinction  between  them  nearly  im- 
practicable ;    so  that  they  form  the  fibro-vascular,  or,  when  a 
single  word  is  used,  the  vascular  system.    To  this  system,  also, 
pertain  specially  differentiated  cells,  such  as  cribrose-cells,  in  the 
bark,  etc. 

194.  All  these  are  developed  in  or  among  the  fundamental 
or  untransformed  cells,  and  originate  from  the  differentiation  of 
some  of  them. 

195.  The  fundamental  or  typical  cells  may  therefore  be  said 
to  constitute  the  fundamental  system ;  which  may  also  be  con- 
veniently called  the  cellular  system,  in  contradistinction  to  the 
vascular. 

196.  In  an  ordinary  leaf  it  forms  all  but  the  framework  of 
ribs  and  veins  ;  in  the  stem  of  a  dicotyledon,  the  outer  bark,  the 
pith,  and  the  rays  which  traverse  the  wood ;  in  that  of  a  mono- 
cotyledon, which  generally  has  a  looser  texture  than  the  last,  it 
is  the  common  mass  through  which  the  definite  bundles  of  the 
vascular  system  are  distributed.      Of  the  fundamental  system, 
the  most  typical  or  unmodified  cells  are  such  as  the  chlorophyll- 
bearing  cells  of  leaves  and  of  the  green  bark  of  stems,  as  well  as 
those  with  uncolored  contents  forming  the  pith,  etc.     Borrowing 
a  word  from  the  old  anatomists,  the  early  investigators  of  vege- 
table structure  called  tissues  composed  of  such  cells  Parenchy- 
ma, perhaps  taking  the  idea  of  the  name  from  leaves  in  which 
the  veins  are  distributed  through  the  softer  parts  as  blood-vessels 
through  the  parenchyma  of  the  glands. 

197.  Parenchyma,  therefore,  is  the  name  of  cellular  tissue 
in  contradistinction   to    fibro-vascular  tissue.      In  its  primary 
sense,  only  comparatively  soft  and   thin-walled  cellular  tissue 


58  MORPHOLOGY   OF  THE   CELL. 

took  this  name,  and  this  is  indeed  typical  parenchyma  ;  but  the 
name  rightly  includes,  as  species  or  varieties,  thicker-walled  and 
even  solidified  tissues  composed  of  cells  similar  in  other  respects 
to  the  type,  as  those  in  the  hard  endosperm  of  seeds. 

198.  A  counterpart  name,  Prosenchyma,  was  employed  to 
designate  tissues  formed  of  elongated  cells,  such  especially  as 
wood-cells  and  bast-cells.      These  being  usually  thick-walled, 
and  those  of  tj'pical  parenchyma  thin-walled,  this  character  was 
brought  into  the  definition ;  that  is,  cells  of  prosencl^-ma  were 
said  to  be  thick-walled  as  well  as  long  and  narrow,  those  of 
parenchyma  thin-walled  as  well  as  isodiametric.     But  this  dis- 
tinction does  not  hold  out  well.     All  fibro-vascular  tissues  are 
thin-walled  at  first,  and  some  remain  so ;  while  portions  of  pure 
parenclryma  ma}-  become  thick-walled,  firm  and  hard,  or  take  on 
every  intermediate  condition.    So  that  prosenchyma  may  be  best 
held  to  denote  tissue  of  the  fibro-vascular  system,  and  typically 
that  formed  of  wood-cells.1 

199.  An  explanation  of  the  mode  of  production,  multiplica- 
tion, and  transformation  of  cells  is  deferred  to  a  later  stage. 
Suffice  it  here  to  advert  to  the  fact  that  even-  phaenogamous 
plant,  originating  in  the  seed,  begins  as  an  isolated  cell,  which 
develops  into  a  globular  cluster  of  parenchyma  cells,  and  grows 
into  the  embryo  or  rudimentary  plantlet,  taking  on  the  shape  and 
degree  of  development  characteristic  of  its  kind.     In  embryos 
which  are  considerably  developed  in  the  seed,  the  axis  and  be- 
ginnings of  the  leaves  are  already  outlined  or   rudimentarily 
indicated  there  ;  in  others  the  indication  takes  place  in  the  early 
stages  of  germination. 

200.  From  this  if  not  from  an  earlier  period   development 
is  no  longer  homogeneous.     A  superficial  la}Ter  of  the  common 
parenchyma  becomes  distinguishable  as  the  epidermis  ;  while  in 
an  inner  zone,  or  at  special  points,  certain  cells  develop  into  ducts 
and  wood-cells  (prosenclryma),  and  thus  are  initially  delineated 
the  outlines  of  the  systems  or  regions  which  are  to  characterize 
the  whole  growth ;  namely,  —  taking  a  dicotyledonous  embryo 
for  the  type,  —  an  epidermal  layer,  a  cortical  layer,  a  fibro-vascu- 
lar zone,  and  a  medullary  portion.     As  stem  and  root  develop, 
these  primordial  tissues  complete  themselves  and  have  only  to 
go  on  growing,  each  after  its  kind  ;  but  at  the  developing  points 
(apex  of  the  stem  and  of  the  root),  as  also  in  special  portions  or 

1  "  Zu  dem  Prosenchym  im  weitern  Siune  kbnnen  wir  auch  die  Gefasst 
ziihlen  "  (Nageli  :  Beitrage,  i.  p.  2). 


CLASSIFICATION   OF   CELLS.  59 

zones,  initial  differentiation  continues.  Here  the  nascent  tissue, 
consisting  of  parenchyma  cells,  multiplying  by  successive  divi- 
sions, and  also  the  nascent  prosenchyma  as  it  forms  and  while 
still  capable  of  further  division,  has  been  named  Meristeni. 

201.  Meristem,  therefore,  is  not  a   kind  of  tissue,   but  the 
nascent  state  or  early  condition  of  any  tissue.     It  is  developing 
parenchyma,  either  multiplying  as  such,  or  differentiating  into 
elongated  forms,  as  for  instance,  in  cambium. 

Leaving  the  processes  of  cell-development  to  be  considered 
under  the  head  of  "Growth,"  and  the  disposition  of  cells  and 
tissues  in  the  fabric  to  be  described  under  the  several  organs 
(root,  stem,  leaf,  etc.)  which  they  compose,  the  kinds  of  cells 
are  here  to  be  indicated,  without  particular  reference  to  their 
arrangement  in  the  plant.  In  all  classifications  of  objects  which 
are  understood  to  have  been  developed  from  one  type,  interme- 
diate forms  of  almost  every  gradation  are  to  be  expected.  It  is 
specially  so  with  plant-cells  ;  and  of  them  it  should  be  said,  once 
for  all,  that  the  kinds  which  have  received  distinct  names,  with 
or  without  sufficient  reason,  are  only  types,  or  leading  modifica- 
tions,—  some  of  a  very  marked,  some  of  a  quite  subordinate 
character.1 

202.  Plant-cells  are  to  be  described  in  this  chapter  under  the 
following  classification  :  — 

I.  Cells  of  the  fundamental  system,  or  parenchyma  cells,  — 
permanent  t}*pical  cells. 

1.  Parenchyma  cells,  strictly  so  called,  including  as  modi- 

fications collench}-ma  cells  and  sclerotic  parenchyma 
cells,  or  grit-cells,  such  as  the  lignified  cells  of  seed- 
coats  and  drupes,  etc. 

2.  Epidermal    cells,   and   their  modifications;   e.  g.,  Tri- 

chomes. 

3.  Cork-cells,  forming  subcrous  parenchyma,  or  cork. 

II.  Cells  and  modified  cells  of  the  fibro- vascular  system,  —  pros- 
enchyma in  the  widest  sense. 
1.   Cells  of  prosenchyrna  proper. 

a.  Typical  wood-cells  and  woody  fibres,  including  libri- 

form  cells  (Sanio),  and  the  secondary  wood-cells 
(De  Bary). 

b.  Vasiform  wood-cells,  or  Tracheids. 

1  Sometimes  a  single  cell  in  a  uniform  tissue  may  develop  unlike  its  neigh- 
bors as  regards  one  or  more  of  the  following  characters  :  form,  size,  nature  of 
cell-wall  or  cell-contents.  Such  cells  are  termed  by  Sachs,  idioblasts. 


60 


MORPHOLOGY  OF   THE  CELL. 


2.  Vessels,  or  ducts. 

a.  Dotted. 

b.  Spirally  marked. 

c.  Annular. 

d.  Reticulated. 

e.  Trabecular. 

3.  Bast-cells,  Bast-fibres,  or  Liber-fibres. 

III.  Sieve-cells,  or  Cribrose-cells. 

IV.  Latex-cells. 

Intercellular  spaces  and  canals  are  neither  cells  nor  tissues, 
but  they  require  consideration  in  connection  with  them. 

I.  Cells  of  the  Fundamental  System,  —  Parenchyma  in  the  -widest 
sense,  including  Modifications  for  Protective  Surfaces. 

PARENCHYMA. 

203.   This  term  is  applied  at  present  to  all  typical  cellular 
tissue  except  that  which  belongs  to  the  epidermal  system.     It 

therefore  constitutes 
the  mass  which  sur- 
rounds fibro-vascu- 
lar  bundles,  forming 
pith,  medullary  rays, 
the  pulp  of  leaves 
and  fruits,  etc.  It 
occurs  in  nearly  all 
parts  of  all  plants. 

The  elements  of 
parenchyma  are  sim- 
ple cells  more  or  less 
separable  from  each 
other,  in  some  cases 
by  slight  pressure, 
and  in  others  by  the 
cautious  use  of  a 
macerating  solution. 

The  cells  vary  greatly  in  form,  but  usualty  are  polyhedral  or 
spheroidal.  Extended  classifications  of  the  cells  themselves, 
based  upon  form,  have  been  made,  but  the}'  are  of  no  utility 
and  of  small  historical  interest.  Yet  three  principal  shapes  may 
well  be  distinguished  ;  namely,  short  or  isodiametric,  elongated, 
and  flattened. 


FIG.  37.  Parenchyma  from  stem  of  Marrubium.    4°.    (Jacolw.) 


PARENCHYMA. 


61 


204.  In  the  youngest  state  of  organs  short  parenchyma  cells 
form  the  whole  mass ;  here  they  are  relatively  small,  filled  with 
protoplasm,   and   have 

no  intercellular  spaces. 
Later  the}'  are  changed 
in  shape  and  size,  may 
have  conspicuous  in- 
tercellular spaces,  and 
the  protoplasm  ma}-  be 
replaced,  at  least  in 
part,  by  other  matters. 

205.  If  the  cells  are 
loosely  aggregated  and 
have    conspicuous    in- 
tercellular  spaces,  the 
tissue  is  called  spongy 
parenchyma.  The  cells 
in  such  cases  are  apt 
to     be    more    or    less 

branched,  and  in  some  plants  assume  regular  stellate  forms. 

206.  Elongated  parenchyma  cells  are  generally  more  com- 
pactly combined  than  the  short  ones.     They  are  well  seen  in  the 

upper  part  of  most  leaves,  where 
the}*  have  received  the  significant 
name  palisade-cells. 

207.  Flattened  parenchyma 
cells  are  the  common  form  in  the 
vertical  plates  (medullary  rays) 
which  radiate  from  the  pith  to 
the  bark  in  woody  plants. 

208.  The  walls  of  typical  pa- 
renchyma cells  are  thin,  and  may 
be  variously  marked  with  pits, 
especially  at  the  points  of  con- 
tact with  other  cells.  Thicken- 
ing threads  forming  reticulations 
and  spirals  are  not  uncommon  ; 
the  latter  occur  in  the  aerial 
roots  of  Orchidaceae.  A  crum- 
pling or  folding-in  of  the  wall  is  seen  in  some  of  the  cells  of  pine 
leaves. 


FIG.  38.   Forms  of  parenchyma  in  leaf  of  Pyrus  roiu munis.     (Jacobs.) 
FIG.  39.  From  pith  of  Sambucus  nigra,  showing  pitted  walls.    (Gris.) 


62 


MORPHOLOGY    OF   THE   CELL. 


209.  Thin-walled  parenchyma  cells  play  an  important  part  in 
assimilating  and  storing,  and  special  names  are  given  to  cells 
which  have  these  offices,  such  as  chlorophyll  parenchyma,  starch 
parenchyma,  etc.     In  the  tissues  of  most  succulents,  and  in  the 
leaves  of  a  few  plants,  some  of  the  parenchyma  cells  are  filled 
with  clear  sap  and  more  or  less  mucilaginous  matter,  and  con- 
stitute the  so-called  water  tissue. 

210.  The  walls  of  typical  parenchyma  cells  consist  of  ordinary 


cellulose  ;  but  even  slight  deviations  from  the  type  furnish  good 
illustrations  of  lignified  and  of  cutinized  membranes. 

211.  Lignification  may  increase  the  thickness  of  the  cell-wall, 
greatly  reducing  the  cell-cavity,  or  it  may  merely  harden  the 
membrane  without  much  thickening.  The  parenchyma  cells 
found  associated  with  other  elements  in  woody  tissues  have 
walls  of  the  latter  character ;  the  grit-cells  in  pears  and  many 
other  fruits  show  good  examples  of  the  former.  Such  hardened 
cells  are  called  sclerotic  parenchyma  cells. 


FIG.  40.  Sclerotic  parenchyma  cells  from  fruit  of  the  pear.    (WtfKt 


ENDODERMIS. 


63 


In  many  cases  it  can  be  shown 
thickened  walls,  as  shown  in 
Fig.  41. ' 

212.  Certain  modified  pa- 
renchyma cells  are  often  united 
to  form  sheaths  around  fibro- 
vascular  bundles.  These  cells 
are  prismatic,  and  in  close 
apposition.  Their  walls  are 
thin,  except  at  their  faces  of 
mutual  contact,  where  they  are 
conspicuously  thickened,  and 
often  plicate,  and  nearly  all 
parts  of  the  membrane  are 
more  or  less  cutinized. 


that  canals  run  through  these 


213.  These  cells  con- 
stitute the  endodermis. 
They  generally  contain  a 
large  amount  of  starch. 

214.  Parenchyma  cells 
ma}*   undergo    the    mu- 
cilaginous   modification 
(see  147),  as  in  the  con- 
ductive   tissue    of    the 
style  of   man}'    flowers 
and  the  albumen  of  many 
seeds.     This  change  is 
common  also  in  the  lower 
plants. 

215.  An  appearance 
closely     resembling     in 
some   points    that    pro- 
duced by  the  mucilagi- 
nous modification  is  pre- 


1  A  second  kind  of  sclerotic  parenchyma  sometimes  accompanies  the  longer 
sclerotic  cells  in  a  few  ferns  and  some  monocotyledons.  Its  cells  appear  as  if 
segments  of  a  jointed  fibre,  somewhat  flattened  on  the  side  next  the  long  cells, 
and  decidedly  convex  on  the  other.  Such  flattened  cells  are  unequally  thick- 
ened on  the  two  sides,  and  the  walls  are  somewhat  silicitied.  But  the  most 
striking  feature  in  many  cases  is  the  deposition  within  the  cavity  of  the  cell 
of  a  mass  of  silicic  acid  ;  this  is  well  seen  in  the  hard  cells  which  accompany 
the  fibro-vascular  threads  in  the  leaves  of  some  palms. 

Fio.  41.    A  sclerotic  cell  from  the  nutshell  of  Juglana  regia.    (Reinke.) 
Fio.  42.    Section  through  the  central  cylinder  of  a  binary  root  of  a  vascular  crypto- 
gam (Cyathea  medullaris).    p,r,r=>  endodermis.    (Van  Tieghem.) 


64 


MORPHOLOGY   OF  THE   CELL. 


sented  by  the  parenchyma  cells  just  under  the  epidermis,  or 
outer  layers  of  cells,  in  many  plants.     The  cell-wall  is  thickened 


very  considerably  at  the  angles,  and  upon  the  application  of 
dilute  acids  swells  greatly,  but  without  becoming  clearly  muci- 
laginous. When  moist, 
such  cells  have  a  bluish- 
white  color  and  a  marked 
lustre.  They  are  known 
as 

216.  Collenchyma  cells. 
They  are  generally  some- 
what elongated,  and  so 
united  as  to  form  threads 
which  possess  great 
strength,  and  are  believed 
to  serve  an  important  me- 
chanical office  in  the  plant 
Good  examples  of  these 
are  afforded  by  the  stems 
of  many  Umbelliferse. 


EPIDERMIS. 

217.  This  is  the  outermost  layer  of  cells  covering  the  sur- 
face of  the  plant.  In  some  of  the  higher  plants  it  persists  with 
little  change  throughout  the  life  of  the  organism  ;  in  others  it  is 

Fm.  43.  Parenchyma  with  walls  which  have  undergone  tho  gelatinous  modification : 
a,  from  the  centre  of  the  style  of  Salvia  scabiosaefolia ;  b.  from  the  stigma  of  Gesneria 
elongata.  (Capus.) 

Fm.  44.  Transverse  section  of  root-stock  of  Smilacliia  bifolln,  chowing  collenchyma 
cells  just  under  the  epidermis,  <•/,.  Note  also  the  ordinary  parenchyma  at  pc,  and  the 
endodermis  at  op.  (Van  Tieghetn.) 


EPIDERMIS.  65 

sooner  or  later  thrown  off,  and  replaced  by  a  subjacent  protective 
tissue,  —  cork. 

218.  Except  at  peculiar  openings  (stomata,  etc.),  the  epider- 
mal cells  are  in  close  apposition.     Upon  their  exposed  surface 
they  are  cutinized,  and  thus  a  continuous  hyaline  lihn  is  formed, 
known  as  the  Cuticle.* 

219.  Sometimes  the  epidermis  may  be  torn  off  without  much 
disturbing  the  underlying  tissues. 

220.  Besides  the  cells  which  compose  the  proper  tissue  of  the 
epidermis,  there  are  certain  ap- 
pendages or  accessory  structures, 

mainly  hairs  or  analogous  pro- 
ductions (together  called  tri- 
chomes),  and  peculiar  cells  which 
constitute  the  stomata. 

22 1 .  Epidermal  cells  proper  are 
in  uninterrupted  contact.     They 
are  usually  of  a  tabular  or  pris- 
matic  form.      The   lines   which 
mark   their   outlines   as  viewed 
from      above      are      sometimes 

straight,  but  oftener  sinuous,  at  least  on  the  longer  sides  of  the 
cell,  which  here  as  elsewhere  correspond  with  the  direction  of 
growth.  Near  stomata  and  trichomes  the  cells  frequently  assume 
very  irregular  forms. 

222.  Their  upper  or  free  surface  is  generally  slightly  convex, 
and  often  has  minute  outgrowths,  for  instance,  in  velvety  petals  ; 
when  these  are  larger  and  longer,  the}-  constitute  the  simplest 
form  of  plant  hairs. 

223.  Delicate  epidermis  possesses  thin  walls ;  but  in  a  large 
number  of  fleshy  and  tough  plants  the  walls  have  considerable 
thickening,  yet  not  alwa}-s  on  the  same  part.    Thus  in  the  leaves 
of  Cycads  the  upper  wall  is  the  thicker ;  in  man}'  Bromeliaceae, 
the  lower  and  side  walls.     In  a  few  cases  the  cell-cavity  is  nearly 
filled  by  the  thickening  material.     Stratification,  striation,  and 
pitting  of  the  cell-wall  may  also  occur,  great  diversity  existing 
in  all  these  respects. 

224.  When  the  epidermis  is  very  delicate,  the  demonstration 
of  the  thin  film  of  cuticle  requires  great  care  in  the  employment 

1  By  De  Candolle  the  term  cuticle  was  applied  to  the  layers  of  epidermal 
cells,  and  not  restricted  to  the  cutinized  film  (Physiologic,  1832,  p.  109). 

FlG.  45.    Stoma  of  Samtmcns  nlgra  surrounded  by  epidermis. 
5 


66 


MORPHOLOGY   OF   THE  CELL. 


of  the  reagents.  According  to  de  Bary,1  the  cuticle  merely 
covers  the  pure  soft  cellulose  membrane  of  the  epidermal  cells 
when  these  are  thin-walled;  but  when  the  walls  are  thicker, 
especially  in  epidermis  which  is  long-lived,  that  part  of  the  cell- 
wall  which  borders  on  the  cuticle  becomes  infiltrated  with  cutin, 
and  thus  there  arise  one  or  more  layers  of  modified  cellulose, 
each  of  which  exhibits  the  reac- 
tions of  cutin.  When  such  cells  are 
treated  with  warm  potassic  hydrate 
(a  ten  per  cent  solution  is,  on  the 
whole,  strong  enough),  the  cutin  is 
slowly  removed,  and  the  cellulose 
wall  remains,  although  with  con- 
siderable loss  of  substance.  Walls 
which  are  thus  impregnated  with 
cutin  in  strata  form  cuticularized 
layers?  The  management  of  a 
warm  solution  of  potassic  hydrate, 
in  order  to  obtain  satisfactory  re- 
sults in  the  demonstration  of  the 
fine  stratification,  demands  much 
care.  It  is  advisable  to  apply  very 
gradual  increments  of  heat  to  the 
glass  slide  in  the  case  of  the  more 
delicate  specimens. 

225.  Waxy  and  resinous  matters 
are  frequently  associated  with  the 
cuticle.  In  some  cases  the  amount 

of  such  substances  is  large,  and  assumes  commercial  importance. 
The  young  leaves  of  the  wax  palm  (Ceroxylon  andicola)  are  said 

1  Vergleichende  Anatomie,  p.  80. 

2  This  division  into  apparent  lamellae  can  be  easily  demonstrated  in  some 
cases  by  the  application  of  chloroiodide  of  zinc,  which  imparts  a  yellowish 
color  to  the  thick  film,  except  at  its  outer  surface.     Mohl  explained  the  struc- 
ture of  the  exposed  cell-wall  in  Viscum  album,  where  the  film  is  very  thick, 
as  follows:  "The  epidermis  cells  consist  here  of  two  or  three  generations 
enclosed  one  within  another,  of  which  all  the  thickened  walls  on  the  outer 
side  have  become  blended  together  into  a  membrane  composing  the  cuticle. 
These  layers  are  to  be  called  the  cuticular  layers  of  the  epidermis,  to  dis- 
tinguish them  from  the  mass  secreted  on  the  outside  of  the  cells,  the  true 

FIG  46.  Transverse  section  of  the  leaf  of  Aloe  verrucosa:  a,  section  in  water,  — the 
non-cuticularized  parts  of  the  membranes  shaded;  above  these  are  the  cuticular 
layers  covered  by  the  cuticle  proper;  &,  section  heated  in  potassic  hydrate;  the  cuticle 
proper  has  been  raised  from  the  cuticularized  layers;  c.  section  boiled  In  potassic  hy- 
drate; cuticle  proper  removed,  epidermal  cells  separated,  cuticular  layers  distinguished 
by  finer  stratification. 


EPIDERMIS.  67 

to  yield  twenty-five  pounds  of  wax  to  each  tree.     Bayberry  wax 
is  a  more  familiar  example. 

226.  To  such  waxy  coatings  is  due  the  glaucous  appearance 
of  the  leaves  and  fruits  of  many  plants.    The  coatings  are  chiefly 
of  the  following  kinds  (de  Bary J)  :  — 

1.  Coherent  layers  or  incrustations  upon  the  epidermis.  2. 
Crowded  vertical  rods  of  considerable  length,  as,  for  instance, 
those  on  the  internodes  of  Saccharum  offlcinarum,  from  ten  to 
fifteen  hundredths  of  a  millimeter  in  height.  3.  Very  short 
rods  or  rounded  grains.  These,  on  the  leaves  of  Tropseolum, 
are  not  very  near  together,  but  on  those  of  the  cabbage,  tulip, 
etc.,  are  more  crowded.  4.  When  the  grains  are  more  minute, 
and  have  the  shape  of  needles  irregularly  massed  together,  they 
constitute  the  peculiar  bloom  of  the  leaves  of  Eucalyptus, 
Ricinus,  etc. 

227.  Between  the  above  kinds  there  are  many  intermediate 
ones,  Agave  Americana,  for  instance,  furnishing  forms  between 
the  two  last  named. 

228.  Epidermal  cells  proper  have  a  delicate  lining  of  proto- 
plasm and  a  distinct  nucleus.    The  cell-sap  is  generally  colorless 
and  transparent,  allowing  light  to  pass  with  very  little  obstruc- 
tion to  the  layers  beneath  the  epidermis ;   but  in  some  cases 
it   is  so  colored  as  to  impart  a   conspicuous  hue  to  the  plant. 
In  many  water-plants  there  is    no  well-marked  distinction  be- 
tween epidermis    and   the    subjacent    tissue,  even   the  cells  of 
the  upper  layer  containing  chlorophyll,  but  epidermal  cells  are 
mosth*  free  from  either  chlorophyll  or  starch.     Brongniart  has 
shown  that   some   amphibious   plants   have    chlorophyll   in  the 
epidermal  cells  of  the  aquatic  but  not  of  the  terrestrial  form. 
That  the  rule  is  not  universal  is  shown  by  Callitriche,  which, 
according  to  Hegelmaier,  has  epidermis  without  chlorophyll  in 
both  forms. 

229.  Epidermis  usually  consists  of  only  one  stratum  of  cells, 
but  it  may  be  made  up  of  two,  three,  or  even  more  layers. 
Division  of  the  original  epidermal  cells  by  one  or  more  partitions 
parallel  to  the  surface  of  the  leaf  gives  rise  to  superposed  cells  ; 
and  thus  multiple  epidermis  results,  as  in  the  upper  surface  of 

cuticle,  which  is  soluble  in  caustic  potash,  and  in  most  cases  forms  but  a  very 
thin  coating  over  the  epidermal  cells"  (Veg.  Cell,  Henfrey's  trans.,  p.  35). 
Good  examples  for  study  of  the  different  kinds  of  cuticular  infiltrations  are 
afforded  by  the  following,  —  leaves  of  Dianthus  caryophyllus,  Galanthus  nivalis, 
Ilex,  Pinus,  Hoya,  Sassafras,  and  Taxus,  and  twigs  of  Viscum  and  of  Oleander. 
1  Botanische  Zeitung,  1871. 


gg  MORPHOLOGY   OF   THE   CELL. 

the  leaves  of  many  species  of  Peperomia,  Ficus,  and  Begonia. 
Multiple  epidermis  is  not  always  of  even  thickness  throughou t; 
sometimes  a  portion  may  be  only  one  or  two  cells  thick,  while 
adjacent  portions  are  composed  of  many  layers.  Such  differ- 
ences  are  generally  associated  with  the  occurrence  of  stomata, 
hairs  etc  The  subjacent  cells  in  some  forms  of  multiple  epi- 
dermis are  smaller  than  those  above  them,  and  in  these  cases 
the  arrangement  of  the  cells  in  the  successive  layers  presents 

striking  inequalities. 

230.  Trichomes.      tinder 
this  term  are   included  the 
multifarious  forms  of  hairs, 
scales,  bristles,  and  prickles. 

Hairs  are  sometimes  of 
diverse  forms  on  the  same 
plant,  and  even  on  the  same 
part,  but  sometimes  so  pecu- 
liar and  uniform  throughout 
large  genera,  or  even  orders, 
that  they  aid  in  their  iden- 
tification; as,  for  instance, 
in  Malpighiacese,  Loasacese, 
and  Elaeagnaceae. 

231 .  Simple  hairs,  whether 
branched  or  unbranched,  are 
formed  by  the  prolongation 
of  a  single  epidermal  cell, 
either     slight,     forming     a 
mere  papilla,  or  to  a  great 
length,   as  in  the   so-called 
fibres    of    cotton.       Simple 
hairs  are  abundant  upon  the 
rootlets  of  most  plants  at  a 
little  distance  behind  the  ad- 
vancing tip,  where  they  play  an  important  part. 

232.    Compound  hairs  are  of  all  degrees  of  com- 
plexity.    They  may  start  from  a  single  cell,  or  from 
a  group  of  cells,  and  may  have  the  derivative  cells 
47  a        arranged  in  many  ways.     The  cells  at  or  near  the 

FIG.  47  a.  Upper  portion  of  a  glandular  hair  of  Martynia  proboscidea.   T-  (Martinet  ) 
PIG.  47  t>.  View  from  above,  of  the  upper  portion  of  the  same.     »?".    (Martinet  ) 
FIG.  48.  Cynoglossum  officinale.    Longitudinal  section  through    a  young  angular 
bristle  at  the  beginning  of  the  thickening.    =4*.    (Strasburger.) 


TRICHOMES. 


69 


foot  of  the  hair  may  differ  somewhat  in  shape,  size,  and  arrange- 
ment from  the  other  epidermal  cells.     They  may  form  an  emi- 
nence upon  which  the  foot  rests,  or  they  may  be  somewhat 
sunken  so  that  the  body  of  the  hair 
hardl}"  reaches  the  general  surface  of 
the  epidermis ;  but  usually  the  hair 
projects  for  a  considerable  distance 
above  the  border  of  the  depression. 

Both  simple  and  compound  hairs 
may  be  variously  curved  and 
branched,  giving  rise  to  stellate  and 
many  other  forms. 

233.  Scales  are  trichomes  which 
are  mostly  compound,  and  consist 
of  discs  borne  by  their  edges  or  cen- 
tres, either  with  or  without  a  short 
foot  or  stalk.     If  the  disc  is  com- 
posed of  radiating  cells,   the  scale 
becomes  stellate,  a  form  which  re- 
sembles or  passes  into  the  stellate 
and  tufted   hairs  common  in  Mal- 
vaceae,  etc.     Well-marked   stellate 
scales  are  met  with  in  Oleacea?  and 
Elaeagnaceae. 

234.  Bristles^  prickles  and  epidermal  spines  are  firmer  or 
stouter  outgrowths.    When  such  outgrowths  are  truly  epidermal, 
the}-  come  off  with  the  epidermis. 

Hairs,  scales,  and  prickles  differ  very  greatly  as  to  their  per- 
sistence, some  being  exceedingly  short-lived,  as,  for  instance, 
the  hairs  which  occur  on  roots  ;  while  others,  for  instance  the 
prickles  on  the  rose,  last  for  long  periods. 

235.  In  certain  outgrowths  from  the  edges  of  leaves  or  else- 
where the  structure  is  complicated  by  the  presence  of  a  portion 
of  the  underlying  framework.     This  is  notably  the  case  in  the 
fringe  upon  the  leaves  of  Droseraceae.     There  are  all  degrees  of 
variation  between  such  trichomatous  outgrowths  and  spinulose 
teeth,  or  lobes. 

236.  The   consistence   of  the   cell- wall   in   trichomes  varies 
widely,  from  extreme  tenuity  to  the  density  of  a  silicified  wall. 
The  more  delicate  hairs  are  transparent,  so  that  the  contents 


Fro.  4!>.    Branching  unicellular  hairs:  a,  from  Huraulus  (the  hop);  6,  stellate  hair 
of  Deutzia.    (Van  Tieghem.) 


70 


MORPHOLOGY   OF   THE   CELL. 


238.    Stomata. 


can  be  plain!}7  seen,  thus  affording  opportunity  for  examining 
the  movements  of  protoplasm,  and  for  the  study  of  the  effects 
of  reagents  upon  the  contents  of  cells. 

Young  hairs  contain  much  protoplasmic  matter;  at  a  later 
stage  they  have  a  large  proportion  of  cell-sap ;  still  later  many 
are  filled  onty  with  air. 

237.  At  first  the  epidermis  is  always  completely  continu- 
ous, the  cells  being  in  close  contact  with  each  other;  but 
soon  there  appear,  especially  in  leaves,  guarded  openings 
through  which  the  interior  of  the  plant  is  brought  into  com- 
munication with  the  surrounding  atmosphere.  These  apertures 
are  of  two  principal  kinds,  the  most  important  and  widely  dis- 
tributed being 

These  are  combinations  of  epidermal  cells  of 
a  peculiar  character,  between 
which  a  narrow  slit  extends 
directly  through  the  epidermis 
to  an  intercellular  space  be- 
low. The  cells  bordering  the 
slit  are  well  termed  guardian 
cells,  on  account  of  their 
opening  and  closing  under 
certain  circumstances.  The 
neighboring  epidermal  cells 
are  frequently  arranged  in  a 
definite  order ;  and  the  po- 
sition of  the  stoma  has  in 
many  cases  a  plain  relation  to  the  underlying  framework. 

Stomata  belong  especiall}*  to  green  organs  exposed  to  the  air  ,- 
but  they  have  been  detected  on  all  superficial  parts  of  the  plant, 
with  the  exception  of  roots.1 

239.  Viewed  from  above,  stomata  appear  generally  as  elliptical 
bodies  through  which  runs  a  narrow  slit  in  the  direction  of  the 
longer  diameter.  Each  guardian  cell  is  therefore  half  the  ellipse. 
The  cleft  varies  in  width  according  to  certain  external  condi- 


1  The  following  cases  are  cited  by  de  Bary  (Vergl.  Anat.,  p.  49)  :  On  rhizo- 
mata  and  tubers  (young  potatoes),  on  the  perianth,  the  anther  (in  Lilium 
bulbiferum),  on  the  pistil,  on  the  seed-coat  (Canna).  Plants  destitute  of  chloro- 
phyll may  also  be  destitute  of  stomata,  as  in  Mouotropa  Hypopitys  ;  or  have 
them  only  on  the  pistil,  as  in  Lathi-sea. 

Fio.  CO.    Adult  8toma  of  Hyacinthus  orientalls,  seen  from  above.    (Strasburger.) 
Fio.  51.    The  same,  seen  from  below. 


STOMATA. 


71 


tions  hereafter  to  be  described,  the  stoma  being  in  fact  a  deli- 
cately balanced  valve.  A  vertical  section  shows  that  the  outer 
part  of  the  opening  is  wider  than  the  narrow  passage  farther 
down,  and  that  the  space  below  this  widens  somewhat  towards 
the  intercellular  cavity.1 


1  The  following  table,  compiled  from  figures  given  by  Weiss,  gives  the  num- 
ber of  stomata  on  the  upper  and  under  sides  of  the  leaves  of  various  plants 
for  the  most  part  readily  procurable  by  students.  To  show  the  wide  differences 
in  size,  the  longer  and  shorter  diameters  have  been  added,  and,  finally,  the  frac- 
tion of  a  square  millimeter  covered  by  a  single  stoma. 


Name  of  plant. 

Number  in 

S'[.  111  111. 

! 

5 

The  space  in  a 
sq.  mm.  covered 
by  a  stoma. 

B 

3< 

& 

i* 

0 
31 
0 

171 
0 
67 

48 

0 
0 
219 
0 

0 
0 
30 

176 
0 
0 
0 
0 
0 

138 
0 

460 
142 
60 
101 
0 
65 
0 

0 
71 
60 
128 
0 
0 
0 
94 

228 
82 
400 
193 

67 
191 

27 
229 
237 
301 
208 
43 
259 
146 
65 
297 
325 
330 
212 
461 
62 
251 

302 
480 
0 
0 
71 
216 
382 
270 

145 
26 

82 
166 
263 

330 
477 
405 
158 

0.047 
0.042 
0.024 
I  0.012 
i  0.026 
0045 
0.026 
(0.054 
{  0.060 
0.033 
0.029 

0.032 
0.042 
0.027 
0.028 
0.034 
0045 
0.034 
0.020 
0.029 
0.024 
0.071 
0.022 
(  0.017 
{  0.026 
(  0.018 
||  0.029 
1  0.026 
j  0.051 
0.034 
0.024 
0031 
(0035 
{  0.033 
!  0.036 
i  0.051 
0.053 
0.033 
I  0.021 
0.029 
0.028 
0.029 
0.024 
0.037 

0.031 
0.027 
0.017 
J  0.012 
1  0.017 
0.040 
0.018 
(0.035 
10.050 
0.022 
0.018 

0.031 
0.034 
0.018 
0.019 
0.022 
0.032 
0.023 
0.019 
0.025 
0018 
0.050 
0.016 
(0.009 
j  0.015 
(0.008 
{  0.021 
0.022 
0.032 
0.023 
0.017 
0.027 
(0.024 
i  0.021 
0.025 
0029 
0.033 
0.021 
0.014 
0.026 
0.016 
0.018 
0.016 
0.029 

0 
0.0276 
0 

0.0195 
0 
0.0247 
0.0706 
0 
0 
0.1137 
0 
0 
0 
0 
0.0176 

0.1074 
0 
0 
0 
0 
0 

0.0164 

0 
0.2070 
0.1945 
0.0307 
0.0323 
0 
0.0363 
0 
0 
0 
0.0386 
0.0139 
0.0758 
0 
0 
0 
0.0792 

0.2T.60 
0.0731 
0.1280 

0.0672 

0.0947 
0.0702 

0.0554 

0.1305 
0.0972 

0.0942 
0.0482 
0.0989 
0.1187 
0.0323 
0.3356 
0.1995 
0.1015 
0.1206 
0.1563 
0.1751 
0.0695 

0.0927 
0.0547 

0.0436 
0.0691 
0.2494 

0.1471 

0.1026 
0.0269 
0.1434 
0.0905 
0.0607 

0.1162 
0.1961 
0.1223 
0.1332 

Acer  Pseudoplatanna,  L.     .    . 
Amarantus  caudatus,  L.      .    . 
Anemone  nemorosa,  L.    .    .    . 
Asclepias  incarnata,  L.    .    .    . 
Aveua  sativa,  L  

Berberie  vulgaris,  L  
Betula  alba,  U    
Brassica  oleracea,  L  
Buxus  sempervirens    .... 
Caltha  palustrls,  L  
Euphorbia  Cyparissias,  L.  .    . 
Ficus  elastica  

Galanthus  nivalis.  L   .    .    .    . 
Geranium  Robertianum  .    .    . 
Helianthus  animus,  L.     .    .    . 
Hydrangea  quercifolia,  Bertr. 
Ilex  Cassine    

Lilium  bulbiferum,  L.      .    .    . 
Maclura  aurantlaca,  Nutt.  .    . 
Mimosa  pudica,  L  

Morus  alba,  L  . 
Nymphaaa  alba,  L.  .    . 

Pinus  Strobus,  L  
Pinus  sylvestris,  L.      .... 
Pisum  sativum,  L  

Pittosporum  Toblra,  Ait.     .    . 
Populus  dilaUta,  Ait.     .    .    . 
Ribes  anreum,  Pursh  .... 
Secale  cereale,  L  

Solanum  Dulcamara  .... 
Stellaria  media,  Sm  
Syringa  vulgaris,  L  
Vinca  minor,  L    .    . 

Vinca  minor,  var.  variegata    . 
Zea  Mais,  L.    ....... 

72 


MORPHOLOGY  OF  THE  CELL. 


240.  As  appears  from 
the  following  figures,  the 
first  stage  in  the  devel- 
opment of  an  ordinary 
stoma  is  the  separation 
of  a  part  of  an  epider- 
mal cell  by  means  of  a 
vertical  partition,  thus 
forming  the  mother-cell 
of  the  stoma.  This 
next  divides  by  a  verti- 
cal plane  which  soon 
exhibits  a  narrow  chink. 
The  cells  thus  slightly  separated  at  their  common  wall  may 
by  subsequent  growth 
bring  about  changes 
in  the  relations  of  the 
neighboring  cells. 

In  Sedum,  as  shown 
by  Strasburger,  there 
are  preparatory  divi- 
sions in  different  di- 
rections, while  in 
some  monocotyledons 
there  are  simultaneous 
divisions  in  contigu- 
ous epidermal  cells. 

241.  Stomata  are 
not  present,  at  least 
in  a  perfect  form,  in  any  submerged  plant.  In  aquatics  with 


FIG.  52.  Vertical  section  of  stoma  of  Hyacintkus  orientalis.    (Strasburger. ) 
FIG.  53  a,  6,  c.    Three  stages  in  the  development  of  the  stomata  of  Sedum  spurium. 
Pig.  53c  shows  the  narrow  slit  made  by  the  neighboring  epidermal  cells.    (Strauburger.) 


STOMATA. 


73 


floating  leaves  they  are  confined  to  the  upper  surface  of  the 
leaf.  The  leaves  of  certain  plants,  as  those  of  monocotyledons 
and  those  which  take  a  vertical  po- 
sition, have  them  in  nearly  equal 
numbers  on  the  two  sides ;  but  in 
most  cases  the  number  on  the  under 
exceeds  that  on  the  upper  surface, 
as  will  be  seen  from  the  table  on 
page  71.  As  regards  the  approxi- 
mate number  on  leaves  of  average 
size  in  some  of  our  common  plants, 
the  following  figures  may  be  of 
interest :  — 

Nymphsea 7,650,000 

Brassica  oleracea 11,540,000 

Helianthus  animus 13,000,000 

242.  Water-pores.   Directly  over  the  extremities  of  the  fibres 
of  the  framework  of  many  green  leaves  are  found  apertures  in 


the  epidermis  which  have  no  true  guardian  cells,1  but  which 
closely  resemble  ordinary  stomata  in  most  other  respects.   Owing 


1  That  is,  the  bordering  cells  do  not  close  under  external  influences. 

FIG.  54.  Vertical  section  of  storna  of  Sedum  spurium.    (Strasburger. ) 
FIG.  .">.  Water-pores  in  leaf  of  Rochea  coccinea.    The  left-hand  figure  shows  both 
an  ordinary  stoma  (the  lower  one)  and  a  water-pore  (the  upper),  as  seen  on  upper  surface 
of  leaf.    The  right-hand  figure  shows  the  structure  displayed  by  a  vertical  section.  (Van 
Tieghern.) 


74  MORPHOLOGY  OP  THE  CELL. 

to  the  fact  that  their  cavity  answering  to  the  intercellular  space 
of  a  stoma  is  often  filled  with  water  instead  of  air,  these  have 
been  called  water-pores.  At  certain  times  liquid  water  passes 
through  these  pores,  collecting  at  the  opening  and  sometimes 
leaving  there,  upon  evaporation,  slight  incrustations  of  calcic 
carbonate.  Water-pores  assume  different  forms  and  vary  much 
in  size.  Good  examples  are  afforded  by  many  Aroideae,  by  the 
teeth  of  the  leaves  in  some  species  of  Fuchsia,  the  leaf-margins 
in  Tropaeolum,  etc.1 

Small  rifts  of  nearly  the  same  shape  can  be  found  in  certain 
grasses ;  but  in  these  the  aperture  comes  from  a  mechanical  rup- 
ture,2 and  the  underling  structure  is  very  simple.' 

CORK. 

243.  This  protective  tissue  is  formed  beneath  and  replaces 
epidermis  in  the  older  superficial  parts  of  plants ;  it  also  con- 
stitutes the  films  by  which  wounds  are  healed.     Only  the  inner 
layers  of  cork-tissue  possess  cellular  activity,  those  which  lie 
outside  of  them  having  perished  :  the  former  contain  protoplasm 
and   are   capable   of  cell-division ;   the  latter  contain  air,  and 
occasionally  small  clusters  of  crystals.     The  inner,  active,  and 
growing  layers  are  known  as  cork  meristem,  cork  cambium,  or 
Phellogen  ;  the  outer,  produced  from  this  and  no  longer  living, 
make  up  the  bulk  of  the  outer  bark,  and  are  ordinarily  called 
cork.     Although  the  older  cork-tissues  must  be  further  described 
in  Chapter  III.,  under  "Bark,"  their  elements  may  be  conven- 
iently treated  of  now  in  connection  with  the  cells  which  produce 
them. 

244.  Origin.   Cork  may  arise  from  several  different  sources, 
the  principal  of  which  are  the  following:   (1)   from  division  of 
cells  in  the  epidermis  (e.  g.,  species  of  Pyrus,  Salix,  Viburnum, 
etc.) ;  (2)  more  commonly  from  underlying  parenchyma,  in  a  few 
cases  even  from  that  which  occurs  in  the  inner  bark  (the  bast 
parenchyma),  as  in  Vitis  and  Spiraea;   (3)  from  parenchyma  at 
injured  surfaces,  as  in  the  healing  of  wounds. 

245.  It  is  normally  produced  upon  the  stems  and  roots  of 
flowering  plants,  especially  dicotyledons.     Its  cells  are  generally 

1  For  a  full  account  of  water-pores,  see  de  Bary's  Anatomic,  p.  54,  and 
Jahrb.  konigl.  botan.  Garten,  Berlin,  1883. 
a  De  Bary  :  Anatomie,  p.  57. 
•  Gardiner :  Proceedings  Camb.  Phil.  Soc.,  1883. 


CORK. 


75 


formed  by  the  division  of  the  mother-cell  into  two  tabular  cells,  by 
a  partition  parallel  to  the  surface  of  the  organ.  In  most  cases 
the  outer  cell  becomes 
cork,  while  the  inner  re- 
tains  its  power  of  division 
and  in  turn  produces  new 
cells.  But  with  the  first 
appearance  of  the  cork- 
layer  a  change  takes  place 
in  all  layers  lying  to  the 
outside  of  it :  they  are  cut 
off  from  nutritive  supplies 
and  soon  die.  The  con- 
tinuous layers  of  cork  are 
called,  collectively,  Peri- 
derm,  a  name  restricted 
by  Mohl  to  tough  cork  in 
distinction  from  soft  cork, 
but  now  employed  with  a 
wider  signification. 

246.  Cork  meristem 
gives  rise  to  successive 
layers  of  cork-cells :  if  the 
new  layers  differ  much 
from  the  preceding  in  the 

shape  and  size  of  their  cells,  an  appearance  of  stratification 
naturally  results.  Cork  meristem  ma}-,  in  exceptional  instances, 
produce  on  its  inner  side  permanent  parenchyma,  the  cells  of 
which  contain  chlorophyll ;  these  green  layers  are  called  Phel- 
loderm,  and  are  observed  well  in  the  beech,  willow,  etc.  (see 
Chapter  III.). 

247.  Cork-cells  are  tabular,  or  sometimes  cubical,  and  with 
few  exceptions  have  no  intercellular  spaces.    In  the  case  of  very 
flat  cells  which  cohere  more  firmly  laterally  than  in  the  line  of 
the  radius,  the  cork-tissue  may  be  readily  separated  in  films  or 
sheets. 

248.  The  walls  of  older  cork -cells  are  cutinized  or  suberizcd 
throughout.     The  demonstration  of  cellulose  in  cork-cells  is  not 
possible  unless  the  cells  have  been  first  acted  on  by  solvents, 


Flo.  56  Formation  of  cork  in  a  branch  of Ribes  nigrum,  one  year  old;  part  of  trans- 
verse section:  h,  hair;  e,  epidermis;  pr,  cortical  parenchyma,  somewhat  distorted; 
K,  the  total  product  of  the  phellogen  c;  k,  cork-cells;  pd,  phelloderm;  b,  bast-cella. 
I  Sachs.) 


76 


MORPHOLOGY  OF  THE  CELL. 


such  as  caustic  potash,  and  the  like.     But  sometimes  the  cell- 
wall  seems  to  be  completely  changed  into  cork-substance. 

249.    Cork-substance  behaves  towards  reagents  in  nearly  all 
respects  as  cutin  does  (see  157). 


250.  Cells  which  have  been  completely  suberized  can  be  sepa- 
rated from  each  other  by  the  gradual  action  of  Schulze's  macer- 
ating solution.1 

251.  The  color  of  cork-cells  is  not  dependent  upon  the  amount 
of  the  change  of  the  wall  into  cork-substance.     The  walls  of  the 
cells  in  some  species  of  willow  are  colorless,  while  those  in  other 
species  are  distinctly  yellow  ;  and  yet  the  former  have  been  as 
thoroughly  changed  into  cork-substance  as  the  latter. 


II. 


Cells  of  the  Fibro-vascular  System,  —  Proseiichyma  in  the 
•widest  sense. 


252.  The  cells  and  modified  cells  of  this  system  constitute 
the  framework  of  a  plant.  In  a  few  of  the  higher  and  in  many 
of  the  lower  plants  it  is  barely  if  at  all  developed,  the  entire 
structure  consisting,  in  such  cases,  of  a  mass  of  parenchyma 
covered  by  epidermis.  But  in  most  plants  it  exists  as  a  skeleton 


1  This  fact  has  led  to  the  belief  that  there  exists  in  such  cases  an  interme- 
diate plate  which  differs  in  its  character  from  the  rest  of  the  cell-wall  ;  but 
prolonged  action  of  the  same  reagent,  especially  with  warming,  causes  the  cells 
to  break  down  and  ultimately  form  a  disorganized  mass. 

Fio.  57.  Formation  of  cork  and  secondary  cortex  in  Betulaverrucosa.  A,  B,  C,  Dt 
•nccettsiro  Htage*;  1,  tlrnt  layor  of  secondary  cortex;  2,  layer  which  divides  In  /*,  to  give 
CHUM  !••  tin-  lirst  layer  of  curk  (shown  in  C),  and  a  layer,  3,  within,  which  again  divide* 
in/'.  (Sauio.) 


WOOD-PAKEKCHtfMA.  77 

bringing  all  parts  into  closer  relations,  and  strengthening  the 
whole. 

253.  The  cells  are  normally  of  considerable  length  in  pro- 
portion to  the  transverse  diameter,  and  are  generally  more  or 
less  sharply  pointed  (prosenchyrna  proper).     The  most  impor- 
tant of  the  modified  cells  belonging  to  this  system  unite  to  form 
long  rows  in  which  the  terminal  partitions  are  nearl}-  or  quite 
obliterated,  throwing  the  cavities  into  one,  and  thus  forming  a 
cylinder,  termed  a  duct.     Between  proper  prosenchyma  cells 
and  ducts  there  are  numerous  connecting  forms  which  render 
impossible  any  attempt  at  classifying  them  exactly.1 

Associated  with  these  cells,  but  differing  in  some  important 
particulars,  are  cribrose  and  latex  cells,  which  for  convenience 
are  here  to  receive  separate  treatment. 

254.  Before  developing  the  provisional   classification  given 
on  page  59,  attention  must  first   be  directed  to  the  peculiar 
transitional  forms  constantly  met  with,  which  belong  as  much 
to  parenchyma  as  to  prosenchyrna,  but  are  more  conveniently 
examined  in  connection  with  the  associated  wood-elements. 

Chief  among  these  intermediate  forms  must  be  mentioned 
those  of  which  Fig.  58,  No.  9,  may  be  taken  as  a  represen- 
tative. Here  the  whole  structural  element  is  isolated  as  an 
elongated  combination  of  three  cells,  one  of  which  has  flattened 
ends,  while  the  other  two,  attached  to  these  ends,  have  their 
free  extremities  pointed.  In  spite  of  their  form,  such  cells  are 
usually  described  as  wood-parenchyma  cells.  When  their  walls 
are  thicker,  they  are  not  easily  distinguishable  from  septate 
libriform  cells  (see  263). 

255.  The  forms  shown  in  Fig.  59,  No.  19,  are  common  in 
the  wood  of  many  plants,  notably  the  oaks.     They  are  rela- 
tively small,  have  rather  blunt  extremities  and  thin  walls.    They 
occur  with  these  characters  especially  in  the  autumnal  wood  of 
the  oaks  (see  395),  while  in  the  spring  wood  they  are  apt  to 

1  For  the  satisfactory  study  of  the  relations  of  the  elements  of  prosenchyma, 
very  thin  sections  are  necessary;  but  for  the  examination  of  the  elements  them- 
selves, recourse  to  some  process  of  maceration,  by  which  they  can  be  isolated, 
is  always  desirable.  In  general,  there  is  nothing  preferable  to  Schulze's  solu- 
tion in  any  strength  adapted  to  the  special  case;  it  must  be  remembered  that 
the  slow  action  of  a  dilute  solution  gives  better  results  than  the  more  rapid 
action  of  a  concentrated  one.  If  the  section  to  be  examined  is  first  subjected  to 
the  action  of  the  macerating  solution  of  proper  strength  and  then  thoroughly 
washed,  it  can  be  dissected  at  pleasure  under  a  high  power  of  a  simple  lens. 
This  method  is  always  to  be  preferred  to  the  ordinary  one  of  disintegrating  the 
Whole  specimen  and  obtaining  a  confused  mass  of  separated  cells. 


78 


MOBPHOLOGY   OF   THE  CELL. 


The  latter 


pass  over  into  the  variety  shown  in  Fig.  59,  No.  18. 
are  known  as  "  conjugate  cells." 

PROSENCHYMA   PROPER. 

256.  Typical  wood-cells.  These  are  best  illustrated  by  elon- 
aated,  often  pointed  cells,  of  which  good  examples  are  found  in 
the  cambium  layer  (that  is,  the  layer  of  merismatic  or  formative 


FIG  58.  Drawings  of  wood-elements.  1-7.  Avicennia  up.  1.  Wood-parenchyma 
cells  united  with  each  other;  tangential  section.  2,  3, 4.  Conjugate  wood-parenchyma 
cells  isolated  by  Schulze's  solution.  5,  6.  Portions  of  spirally  striated  Hbriform  fibres 
isolated  by  Schulze's  solution.  7.  The  septum  of  a  duct.  8-12.  Tectona  grandis;  the 
elements  separated  by  maceration.  8.  Conjugate  wood-parenchy ma  cells.  9.  Ordinary 
wood-parenchyma  fibre  10.  Substitute  fibre  11.  Simple  libriforni  fibre.  12.  Sep- 
tate libriform  fibre.  15.  Porlieria  hygrometrica ;  conjugate  substitute  fibres  seen  in 
radial  section.  The  wood-cells  are  omitted  in  order  not  to  confuse  the  diagram. 
37.  Radial  section  through  the  wood  of  Jatropha  Manihot.  38.  Tangential  section 
through  a  libriform  fibre  and  two  cells  from  a  medullary  ray  of  the  same  plant. 
39-42.  Bast-cells  of  Cytisuf.  Laburnum.  39.  Cross-section  through  a  part  of  a  young 
bast-bnndle  acted  on  by  chloroiodide  of  zinc.  40,  41,  42.  Cross-sections  through  young 
bast-cells,  acted  on  by  chloroiodide  of  zinc  (Sanlo  ) 


WOOD-ELEMENTS. 


79 


tissue  just  under  the  bark  of  dicotyledonous  plants).  Their 
walls  are  thin,  and  at  first  nearly  or  quite  free  from  pits  or 
other  markings. 

The}-  grade  into  three  constantly  recurring  forms ;   namely, 
(1)  parenchyma  (see  254)  ;  (2)  attenuated  forms,  often  so  slen- 

14 


der  as  to  deserve  the  name  of  fibres;  (3)  forms  with  peculiar 
markings  at  most  points  of  contact,  and  thus  much  resembling 
ducts  or  vessels. 


FIG.  59.  Drawings  of  wood-elements.  13.  TracheTd  from  Tectona  grandis.  14-18. 
Porlieria  hygronietrica.  14.  Conjugate  substitute  fibres  seen  in  transverse  section. 
16.  Ordinary  substitute  fibre  after  maceration.  17,  18.  Conjugate  substitute  fibres 
after  maceration.  19-22.  Cytisus  Laburnum ;  the  elements  separated  by  maceration. 
19.  Wood-parenchyma  fibre.  20.  Substitute  fibre.  21.  Simple  Hbriform  fibre.  22.  Tra- 
cheTd. 23.  Cross-section  through  the  cambium  and  youngest  wood  of  Cytisus  Labur- 
num. 24-25.  Ducts  from  Mahnnia  Aquifolium.  24.  After  maceration.  25.  Longitudinal 
section.  26-31.  Ducts  from  Hieracium,  separated  by  maceration ;  showing  the  ex- 
tremity only.  32-34.  Ducts  from  Onorpordon  acanthium,  separated  by  maceration. 
35.  Spirally  marked  duct  from  Vitis  vinifera,  after  maceration.  36.  Libriform  fibre 
from  Jatropha  Manihot.  (Sanio.1 


80  MORPHOLOGY    OF  THE   CELL. 

257.  The  drawings  of  wood-elements  represented  in  Figs.  58 
and  59  are  from  Sanio's  work,  and  are  gi\ren  with  his  nomen- 
clature.    The  cells  figured  in  Nos.  10  and  16,  termed  by  Sanio 
substitute  fibres  (German,  Ersatzfasern),  answer  well  to  the  type 
of  prosenchyma.    When  these  cells  are  much  reduced  in  calibre, 
they  are  known  as  libriform  fibres. 

258.  Ordinary  prosenchyma  cells  usually  have  simple  pits,  but 
no  true  spirals.     The  pits  may  be  round,  and  of  the  same  size  as 
those  on  the  ducts  with  which  they  may  be  in  contact,  but  some- 
times they  are  elongated  slits,  and  run  obliquely,  as  shown  in 
Fig.  59.     If  two  of  these  cells  are  in  contact,  processes  may 
extend  from  one  cell  to  corresponding  protrusions  in  the  other, 
and  thus  one  cell  is  united   with  the  next.     63-  careful  macera- 
tion such  cells  can  be  separated,  and  then  each  appeal's  to  have 
one  or  more  rows  of  square  teeth  or  short  tubes.     It  sometimes 
happens  that   the  wall  at  the   end  of  these  intrusive  tubes  is 
broken  down,  thus  allowing  free  communication    between    the 
cells. 

Good  examples  of  substitution  cells  are  to  be  found  in  the 
wood  of  Magnolia,  Liriodendron,  many  Leguminosse,  etc.  They 
are  not  so  common,  however,  as  conjugate  parenchvma  cells  (see 
Fig.  58). 

259.  Woody   fibres   are   of  two   chief  classes:    (1)   those   in 
which  the  narrowed  cavity  is  continuous  throughout  the  whole 
length,  and  (2)  those  which  have  partitions  dividing  it  (sep- 
tate fibres). 

The  first  class  has  been  again  divided  into  two  groups  depend- 
ing upon  the  presence  of  starch,  but  the  division  is  not  wholly 
satisfactory.  The  first  group  comprises  all  those  fibres  which 
have  a  trace  of  protoplasm,  while  those  of  the  second  have  also 
more  or  less  starch,  and  generally  some  tannin. 

All  of  these  woody  fibres  resemble  the  bast-fibres  of  the  inner 
bark  ol  dicotyledons  so  closely  that  they  have  been  well  called 
libriform.  They  are  described  by  Sanio,  from  whose  paper  on 
the  subject  most  of  these  names  are  taken,  as  being  always 
spindle  or  fibre- form,  relatively  strongly  thickened,  and  occa- 
sionally furnished  with  bordered  pits  which  somewhat  resemble 
those  of  vasiform  elements  (264),  but  are  smaller  and  less 
clearly  defined.  They  never  have  true  spiral  markings,  and 
very  seldom  any  spiral  striation.  They  contain  during  the 
periods  of  rest  of  vegetation  in  winter  more  or  less  starch, 
and  perhaps  some  chlorophyll  and  tannin,  but  at  other  times 
only  air. 


LIBRIFORM   CELLS.  81 

260.  The  unseptate  fibres,  the  true  libriform  cells,  are  only 
sparingly  pitted,  except  in  a  few  species  like  Oleander,  where 
they  are  pitted  on  both  the  radial  and  tangential  walls.     The 
pits  are  generally  elongated  and  oblique,  and  according  to  Sauio 
always  running  from  left  to  right. 

261.  The  cell-wall  of  these  fibres  is  always  lignified,  and  pre- 
sents three  layers ;  and  in  some  instances  there  is  also  a  layer 
which  is  plainty  gelatinous,  e.  g.,  in  Betula  and  Alnus.     These 
gelatinized  fibres  are  not  found  in  all  of  the  annual  rings,  nor 
in  all  parts  of  even  one  ring. 

262.  Libriform  cells  are  variable  in  length  in  different  plants ; 
some  of  the  shortest  occurring  in  Daphne  Mezereum,  .14  mm., 
and  the  longer  in  Avicennia,  2  mm.     In  all  cases  they  are  the 
longest  elements  in  the  mass  of  wood.     They  are  generally  sim- 
ple, but  occasionally  branched  cells  are  met  with,  as  in  Tilia  and 
Cladrastis.     They  are  sometimes  irregular!}-  grouped  together, 
sometimes  radiall}-  arranged.     Species  of  Magnolia  exhibit  the 
latter,  Ulmus  the  former,  mode  of  arrangement. 

263.  Septate  libriform  cells  have  sometimes  been  confounded 
with   wood-parenchyma ;    but   Sanio    points   out   the   following 
distinctive   characters :     (1)   they   are    always   thicker    walled ; 
(2)   they  have  oblique  slits,  while  wood-parenchyma  has   only 
roundish  pits ;  (3)  the}'  become  septate  only  after  the  thicken- 
ing has  progressed  to  some  extent,  while  in  wood-parenchyma 
the  divisions  begin  before  the  cambium  cells 1  from  which  it  ia 
derived  have  begun  to  thicken. 

Septate  libriform  cells  are  less  common  than  any  other  woody 
element;  examples,  however,  are  not  rare  in  Vitis,  Hedera, 
and  Rubus. 

264.  Vasiform  elements.     Neither  of  the  two  forms  already 
considered  —  namely,  typical  wood-cells  and  woody  fibres  —  has 
distinctive  spiral  markings  or  true  bordered  pits  (that  is,  dis- 
coid markings)  ;  but  another  important  class  of  wood-elements, 
of  which  mention  must  next  be  made,  is  characterized  b}'  such 
thickenings. 

265.  To  this  class  of  elements   it  is  difficult  to  give  any 
satisfactory  name.     They  have  been  collectively  termed  vascu- 
lar, but  a  large  part  of  them  are  comparatively  short  and  closed, 
and  cannot  be  property  known  as  ducts  or  vessels ;  the  name 
Tracheal   (or  Tracheary),   more  widely  employed,   is  open   to 


1  The  immediate  derivatives  from  the  cambium,  which  are  partly  formed 
woody  fibres,  have  been  termed  cambium  iibres  (Sanio  :  Bot,  Zeit,,  1863), 


82  MORPHOLOGY   OF   THE    CELL. 

the  objection  that  while  it  is  a  significant  term  when  applied  to 
trachea-like  bodies  (ducts)  it  is  a  misnomer  when  applied  to  an 
elongated  cell  wholly  free  from  annular  or  spiral  markings. 

266.  Tracheal  cells  are  of  two  chief  kinds:  (1)  those  which 
are  closed  throughout,  —  at  least  until  a  very  late  stage  of  devel- 
opment;   (2)  those  formed  by  rows  of  cells  which   lose  their 
intervening  partitions,  and  hence  are  thrown  into  a  long  canal, 
or  vessel.     The  former  are  known  as  Tracheids,1  the  latter  as 
Tracheae.;  for  which  terms  may  be  substituted  the  following, 
applicable  in  nearly  all  cases,  —  Wood-cell  and  Duct. 

The  distinctive  markings  of  tracheids  and  tracheae  arc  bordered 
pits,  or  discoid  markings,  and  various  thickenings  of  which  the 
spiral  ma}'  be  taken  as  an  example. 

Tracheids  and  tracheae  further  agree  in  the  following  point : 
when  complete,  the  protoplasmic  mass  disappears,  leaving  gen- 
erally no  trace.  The  cavity  is  filled  in  a  few  cases  with  watery 
fluid,  in  some  with  water  and  air,  but  in  most  with  air  alone. 
Occasionally  other  matters  may  be  found  in  the  trachere,  for  in- 
stance, latex  ;  but  these  are  so  exceptional  as  to  need  no  further 
mention  at  this  point. 

267.  Vasiform  wood-cells,  or  tracheids,  are  elongated  and  taper- 
ing cells,  more  or  less  lignified,  and  having  peculiar  markings, 
the  principal  kinds  of  which,  although  previously  referred  to  in 
133,  require  a  more  extended  treatment  here. 

268.  Bordered  pits,  called  also  areolated  dots  and  discoid  mark- 
ings,  are   ver\-  common,  especially  in  wood  of  gymnosperms, 
where   they  form   a  characteristic   feature   both   in    fossil   and 

1  But  the  term  trachcid,  as  usually  understood,  is  applied  to  wood-cells  with 
peculiar  markings,  next  to  be  described. 

The  following  measurements  bySanio  show  the  difference  between  the  length 
of  some  tracheids  and  the  libriform  cells  in  the  same  plant :  — 

Tracheids.  Libriform  cells. 

Ehamuus  catharticus 28  mm.  .52  mm. 

jEsculus  Hippocastanum 26     "  .43     " 

Daphne  Mezereum 15     "  .21     " 

Ribesrubrum 49     "  .47     " 

Where,  however,  the  tracheids  alone  are  present,  they  are  sometimes  much 
longer ;  for  instance,  in  Staphylea  pinnata,  1  mm.,  and  in  Philadelphus  coro- 
narius,  .85  mm. 

According  to  Sanio,  the  bordered  pits  of  ducts  are  the  same  as  those  of  the 
tracheids,  as  regards  size,  form,  and  usually  as  regards  frequency. 

Occasionally  tracheids  are  found  which  are  plainly  septate.  It  thus  appears 
that  the  tracheids  form  a  gradation  between  true  ducts  and  libriform  cells  with 
bordered  pits. 


BORDERED    PITS. 


83 


recent  plants.     When  the  wood  in  a  pine  stem  is  cut  radially, 
the  flattened  sides  of  the  wood-cells  exhibit  the  dotted  appear- 
ance seen  in  Fig.  60.     The  number  and  mode  of  distribution  of 
the  markings  in  the  wood- 
cells  or  tracheids  of  Co-  a 
niferai  are  so  nearly  con- 
stant,  that   the}'   may  be 
used     with     considerable 
certaint}'  in  the  discrimi- 
nation of  a  few  genera. 

269.     In    a    transverse 
section  of  the  mature  tra- 
cheids the  discoid  mark- 
ings   are   plainly  seen  to 
be  pits  having  an  arched 
border      or       incomplete 
dome,    and   it    is   also 
seen  that  the  thin  spot 
or   pit   is   common    to 
two    contiguous    cells. 
Hence  the  two  domes, 

being  on  opposite  sides  of  a  partition- wall,  have  a  lens  shape, 
and  the  central  perforations  are  nearly  or  exactly  opposite  each 
other  (Fig.  62).  Even  in  the  same  speci- 
men the  bordered  pits  vary  within  com- 
paratively narrow  limits  both  as  regards 
the  size  of  the  disc  and  that  of  the  central 
aperture. 

The  two  domes  making  up  a  single  dis- 
coid marking  are  at  first  separated  b}7  a 
delicate  plate  of  unequal  thickness ;  but 
later  this  middle  lamella  may  be  broken 
down,  and  then  a  free  passage  extends 
from  one  cell  to  the  other. 

The  character  of  the  domes  and  the  mid- 
dle plate  can  be  understood  from  the  ac- 
companying figures  of  sections  of  the  stem  of  Pinus  S3'lvestris 
(Figs.  62  and  63).  According  to  Sanio.  the  sections  should  be 
boiled  in  acetic  acid,  in  order  to  remove  all  cell- contents. 

FIG.  60.  Areolated  or  disciform  markings  of  the  wood-cells  (tracheids)  of  Pinus 
Laricio  :  a,  aspect  of  radial  walls ;  b,  a  transverse  section :  c,  development  of  the 
markings  in  Pinus  sylvestris.  (Sanio.) 

Fir.s.  61  and  62.  Pinus  sylvestris.  Transverse  sections  of  nearly  perfect  and  perfect 
discoid  markings.  (Strasburger.) 


MOKPHOLOGY  OF   THE   CELL. 


The  cambium-cells  and  the  youngest  tracheids  have  uniform 
and  smooth  walls,  but  in  those  next  older  there  appear  thin 
spots,  which  are  well  defined  above 
and  below,  but  not  on  the  sides,  for 
here  the}-  grade  off  into  the  thicker 
part  of  the  wall.  In  the  cells  which 
are  still  older  the  thin  places  take  the 
shape  of  discoid  markings,  and  are 
clearly  seen  in  an)'  radial  view.  Com- 
parison of  radial  with  transverse  sec- 
tions shows  that  at  the  margins  of  the 
thin  places  a  portion  of  the  wall  ex- 
tends as  a  slight  projection  upwards, 
and  partly  over  the  spot.  In  the  more 
mature  form  the  thin  place  is  still  re- 
tained as  a  delicate  plate  separating 
the  two  cells,  but  easily  broken  down 
perhaps  in  further  growth. 

270.  Scalariforni  markings  (see 
134)  are  especially  abundant  in  ferns. 
The  bordered  pits  are  much  elongated, 
and  appear  as  clefts  with  only  narrow 
portions  of  the  wall  between  them 
(Fig.  64  I).  They  often  follow  each 
other  with  as  much  regularity  as  the 
"rounds"  of  a  ladder,  whence  the  name  (from  scalaria,  —  a 
flight  of  steps).  They  are  more  commonly  found  in 

DUCTS. 

271.  Ducts,  or  Tracheae,  are  variously  marked  by  pits,  and 
by  the  thickenings  described  in  Chapter  I.     Some  of  the  more 
common  forms  of  dots  are  shown  in  Fig.  64. 

Spiral,  annular,  and  reticulated  markings  are  all  formed  by 
the  thickening  of  parts  of  the  wall  by  which  narrow  lines  or 
bands  are  produced  on  the  inner  surface.  In  these  cases  the 
portions  of  the  wall  which  are  not  thickened  are  often  of  extreme 
tenuity,  and  break  upon  slight  pressure  or  strain,  permitting  the 
spiral  to  uncoil  or  the  rings  to  separate  (Fig.  64,  s  s'). 

272.  Spiral  markings.      The  number  of  threads  or  narrow 
bands  varies  from  one  to  fifteen  or  even  twenty,  the  latter  in  the 
petioles  of  Musa.1    They  wind,  as  a  rule,  from  right  to  left ; 

1  De  Bary  :  Vergleichende  Anatomic,  1877,  p.  163. 

FIG.  63.  Pinus  sylvestris.  Cross-section  through  the  cambium  and  young  wood-celU. 
(Strasburger.) 


MARKINGS   OK    DUCTS. 


85 


but,  according  to  Mobl,  from  loft  to  right  in  a  few  plants.  Thus 
in  the  wood  of  Vitis  vinifera,  Berberis  vulgaris,  and  sonic  others, 
they  run  from  left  to  right  in  the  ducts  first  formed,  but  in  the 
reverse  direction  in  those  which  are  produced  later.  And  by 
interruption  of  the  spiral  it  may  have  two  directions  in  the 
same  duct,  as  in  those  of  Cucurbita.1  The  steepness  of  the 


spiral  depends  in  part  on  the  age  of  the  cell,  or  vessel,  —  at  least 
in  some  cases.  According  to  Mohl,  "  if  the  vessel  is  developed 
in  an  organ  which  has  already  completed  its  longitudinal  growth, 
the  turns  of  the  spiral  lie  close  together ;  but  if  the  organ  under- 
goes elongation  after  the  completion  of  the  development  of  the 
vessel,  the  turns  of  the  fibre  are  drawn  far  apart  by  the  stretch- 
ing which  the  vessel  suffers ;  consequently  very  loosely  wound 
spiral  vessels  are  usually  found  in  the  posterior  first-formed  por- 
tion of  the  vascular  bundle  nearest  to  the  pith,  while  those  lying 
nearest  the  bark  have  close  convolutions."2 

273.  Annular  and  reticulated  markings  have  been  regarded  as 
mechanical  modifications  of  spirals,  and  it  is  true  that  inter- 
mediate forms  exist  between  these  types.  For  instance,  tightly 
wound  spirals  are  nearly  annular,  and  in  some  cases  there  are 
threads  which  run  either  vertically  or  obliquely  from  one  part  of 
a  spiral  to  the  contiguous  thread.  But  even  in  the  youngest 
states  of  some  ducts  the  markings  appear  as  rings  or  as  a  net- 


1  Mohl  :  Vermischte  Schriften,   1845,   pp.   287,  321,  Ueber  den  Ban  der 
Ringgefasse. 

2  Mohl :  Vegetable  Cell,  Eng.  Trans.,  1852,  p.  19. 

Fio.  64.  Vertical  radial  section  of  hypocotyl  of  Ricinus  communis,  illustrating  differ- 
ent markings  of  ducts;  t'  t,  pitted;  I,  scalariform ;  s'  s,  spiral,  the  spirals  beginning  to 
uncoil.  (Sachs.) 


86  MORPHOLOGY    OF   THE    CELL. 

work.  While,  therefore,  they  may  and  probably  do  have  a 
common  origin  with  spirals,  it  is  not  necessary  to  assume,  nor  is 
it  probable,  that  they  have  resulted  from  mechanical  displace- 
ments of  them.  The  relative  positions  of  the  separate  rings 
may  be  explained  in  the  same  way  as  the  steepness  of  the 
spirals.1 

274.  Cases  are  met  with,  in  which  projections  from  the  wall 
may  extend  nearly  or  quite  across  the  cell-cavity,  somewhat  after 
the  manner  of  beams.  Such  cross-beam  cells  or  ducts  are  called 
trabecular.  A  good  example  can  be  found  in  some  of  the  tracheids 
of  the  leaf  of  Juniperus  communis.2 

1  "  The  notion  was  extensively  held  that  the  spiral  fibre  could  not  follow 
the  expansion  which  the  vessel  underwent  during  its  growth,  and  tore  up  into 
fragments  which  were  again  united  into  rings,  and  thus  brought  about  the 
formation  of  annular  vessels.     Completely  as  this  idea,  which  was  a  contradic- 
tion to  all  observation,  had  been  refuted  by  Moldenhawer,  it  remained  a  stand- 
ing article  in  all  phytotomieal  writings  up  to  Meyen's  Physiologic"  (Mohl  : 
Vegetable  Cell,  p.  21 ). 

2  De  Bary  :  Vergleichende  Anatomic,  p.  171. 

The  following  measurements  of  wood-cells  and  ducts  are  given  by  "Wies- 
ner  (Die  Rohstofie  des  Pflanzenreiches,  1873,  p.  525)  :  — 

Average  diameter  of  wood-cells. 

Rhus  Cotinus 7.5  /*. 

Lonicera  Xylosteon 9.8  " 

Salix  Capraa 11.0  " 

Viburnum  Lantana 22.0  " 

Alnus  glutinosa 25.0  " 

Fraxinus  excelsior 28.0  " 

Average  diameter  of  dncta. 

Hfematoxylon  Carapechianum 112 /A. 

Csesalpinia  Sappan 120  " 

Ochroma  Lagopus 140  " 

Fraxinus  excelsior 140" 

Ulmus  campestris 158  " 

Tectona  grandis 160  " 

Juglans  regia 220  " 

Carya  alba 248  " 

Quercus  sp 200  to  300  " 

The  ducts  in  the  foregoing  examples  are  so  large  that  in  cross-section 
they  can  easily  be  seen  by  the  naked  eye.  The  following  are  considerably 
smaller :  — 

Tilia  sp 60  ft. 

Acer  sp 7\  " 

Alnus  sp 76  " 

Rhus  Cotinus 80  " 

Betula  sp 85  " 


BAST-FIBRES.  87 

275.  Xyloses.     If  a  cell  still  growing  is  in  contact  with  a  duct 
at  one  or  more  of  its  perforations,  the  cell  may  intrude  into  the 
cavity  of  the  duct,  and  to  a  considerable  extent.     Such  intrusive 
growths  are  known  as  Tyloses  (German,  Thvllen). 

If  the  intrusive  portion  of  the  tylosis  further  multiplies,  pro- 
ducing new  cells,  the  cavit\-  of  the  duct  ma}-  contain  a  confused 
mass  of  irregular  cells  of  various  shapes  and  sizes.  Such  masses 
are  often  found  in  the  ducts  of  Quercus  alba,  Q.  castanea,  Q.  ma- 
crocarpa,  Q.  tinctoria,  Q.  virens,  Castanea  vesca,  Carya  alba, 
C.  olivaeformis,  C.  amara,  Juglans  nigra,  Sassafras  officinalis, 
Morus  rubra,  Maclura  aurantiaca,  and  Robinia  Pseudacacia.  In 
the  latter  they  are  especially  striking.1 

BAST-FIBRES  (LIBER-FIBRES). 
(Sclerenchyma  of  many  recent  German  authors.) 

276.  The  name  bast  was  originally  given  to  the  inner  bark  of 
the  linden  (bass-wood),  and  hence  originated  its  use  as  a  prefix 
in  "  bast-matting,"  etc. ;  the  name  liber  was  applied  in  a  more 
general  way.  namely,  to  any  smooth  inner  bark  (upon  which  one 
could  write).     That  which  imparts  strength  to  inner  bark,  mak- 
ing it  of  use  in  the  arts,  consists  of  long  and  tough  cells  with 
very  much  reduced  calibre ;   but  these  are  not  confined  by  any 
means  to  inner  hark.    Owing  to  this  fact,  some  have  thought  best 
to  abandon  the  terms  bast  and  liber  for  such  cells,  and  adopt, 
on  account  of  their  firmness,  a  term  formerl}-  given  to  grit-cells, 
namely,  sclerenchyma ;  the  older  terms,  however,  arc  not  likely 
to  lead  to  confusion,  whereas  the  other  might.     It  is  in  the  bark 
of  dicotyledons  that  liber-cells  or  liber-fibres  occur  most  abun- 
dantly. 

Their  prevailing  shape  is  that  of  a  slender  spindle,  which  may 
taper  simply,  or  may  be  somewhat  forked  at  the  extremity. 

The  following  can  be  seen  only  under  a  lens  :  — 

Euonymus  Europaeus 20  /*. 

Fagus  sp.      . 28  " 

Crataegus  sp 30  " 

Ligustrum  sp 35  " 

Pyrus  communis 40  '« 

1  Mr.  P.  H.  Dudley,  who  communicates  some  of  the  names  in  this  list,  adds 
in  his  note  :  "  So  far  I  have  never  found  any  tyloses  in  ducts  with  scalariform 
markings. " 


88  MORPHOLOGY   OF   THE   CELL. 

Occasionally  fibres  which  arc  very  ranch  branched  are  met  with, 
notably  in  the  leaves  of  Camellia,  for  instance  common  tea ;  see 
Fig.  68.  Generally  the  walls  are  thickened  unevenly,  even  form- 
ing conspicuous  projections  into  the  cavity  of  the  cell ;  while 
some  fibres  have  regular  and  characteristic  markings,  a  few 


of  which  are  shown  in  Fig.  65.  Septate  forms  are  occasionally 
found.  The  change  in  the  character  of  the  cell-wall  which  ac- 
companies the  thickening  is  essentially  lignitication,  like  that 
observed  in  wood-cells  and  ducts.  It  is  generally  said  that  the 
walls  of  liber-cells  are  less  brittle  than  those  of  the  elements 
of  wood,  and  this  is  commonly  so ;  but  there  are  some  flexible 
wood-elements,  and  there  are,  on  the  other  hand,  some  very 
brittle  fibres  of  sclerenchyma.  The  thickening  of  the  wall  in 
liber-cells  takes  place  not  only  in  different  degrees,  but  with  va- 
riations in  the  amount  of  infiltration  of  foreign  matters,  which 
give  rise  to  differences  in  the  behavior  of  the  fibres  with  reagents. 
In  a  few  cases  the  inner  part  of  the  wall  is  somewhat  gelatinous 


FIG.  65.    Fragments  of  some  of  the  more  common  bast-fibres  used  in  the  arta. 
a.  Flax.  Linum  usitatissimum.    (Wiesner  ) 
6.  Hemp.  CaTinabis  saliva.    (Schaoht.) 

c,  ,Tnte,  Corchorus  capstans.    (Wiesner.) 

d,  China-grass,  Boehmeria  nivea. 


BAST-FIBRES. 


89 


and  possesses  the  power  of  swelling  in  water  and  in  dilute  acids 
(compare  Collenchyma) ;  in  sonic  others  the  outer  part  of  the  wall 
is  gelatinous,  while  the  inner  is  hard.  Morus  alba,  Gleditschia 
triacanthos,  and  Robinia  Pseudaeacia  are  examples  of  the  first, 
Astragalus  falcatus  of  the  second,  condition  (Sanio). 

277.  One  of  the  most  striking  characters  of  the  bast-fibres  of 
many  plants  is  the  abundance  of  crystals  found  therein.  Ex- 
cellent examples  are  afforded  by  the  inner  bark  of  some  of  our 
ligneous  plants  (294). 


278.  The  firm  attachment  of  fibres  to  those  above  and  those 
below  them  has  given  rise  to  erroneous  ideas  relative  to  the 
length  of  single  fibres,  as  the  table  on  the  following  page  shows.1 

By  careful  management  it  is  possible  to  isolate  a  connected 
thread  of  fibres  of  great  length ;  the  value  of  fibres  for  textile 
purposes  depends  largely  upon  this  fact. 


1  The  table  on  page  90  has  been  compiled  from  data  given  by  Wiesncr  and 
also  by  Vetillart,  which  are  here  rearranged  for  greater  convenience  of  refer- 
ence. 

Fio.  66.  Fibre  of  Agave  Americana :  a  and  b,  *f  ;  c,  *f  °.  Only  the  upper  part  of 
each  fibre  is  shown  in  the  left-hand  figures.  The  right-hand  figure  shows  a  cross-section 
of  a  group  of  cells. 

FIG.  67.  Fibre  of  Coir  (Cocos  nucifera) :  a  and  c,  «f ;  b,  »f «.  a  shows  three  separate 
and  complete  fibres,  b,  the  upper  part  of  a  single  one,  c,  a  cross-section  of  a  group  of 
cells. 

Fio.  68.  Transverse  section  through  leaf  of  Camellia  (Thea)  viridis,  showing: 
a,  epidermis;  b,  branched  liber-cell;  d,  oil-drop;  e,  crystals.  (Mirbel.) 


90 


MORPHOLOGY    OF   THE   CELL. 


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CKIBROSE-CELLS. 


91 


ITT      Cribrose-cells.  Sieve-cells,  or  Sieve-tubes. 

279.  In  the  inner  bark  of  stems  of  dicotyledons  with  normal 
structure  certain  long  cells  of  peculiar  character  are  found  as- 
sociated with  bast-fibres.  They 
are  of  tubular  or  prismatic  form, 
and  are  characterized  by  the  pres- 
ence of  circumscribed  panels  in 
the  walls,  in  which  are  numerous 
fine  perforations  permitting  com- 
munication between  contiguous 
cells.  The  panels  are  known  as 
sieve-plates  ;  the  perforations,  as 
sieve-pores.  These  cells  consti- 
tute an  essential,  though  by  no 

means  always  a  conspicuous,  element  of  fibro-vascular  bundles. 

Taken  collectively, 
•"I  they  may  be  known 
as  cribriform  tissue. 
By  their  union  end  to 
rnd  they  appear  like 
long  tubes  with  the 
continuity  interrupted 
here  and  there  by  cross 
partitions.  These  par- 
titions which  separate 
the  individual  cells 
are  sometimes  nearly 
horizontal,  but  more 
generally  oblique,  as 
shown  in  the  annexed 
figures  where  they 
mostly  cut  the  lateral 
wall  of  the  cell  at  a 
sharp  angle. 

280.  The  walls  of 
cribrose-cells  are 
never  lignified  ;  on 
the  contrary,  they  are 

FIG.  69.  PInus  sylvestris.  Face  view  of  radial  wall  containing  two  cribrose-plates 
wholly  deprived  of  callus.  **?*.  (Janczewski.) 

FIG.  70.  Finns  sylvestris.  Radial  wall  of  a  young  tube,  face  view.  The  future  cri- 
brose-plates are  composed  of  callus-cylinders,  filling  tlie  meshes  of  a  cellulose  network. 
llf*.  (Janczewski.) 

FIG  71     Cribrose-cells  in  Vitis  vinifera ;  A,  transverse  anastomosis  of  two  cribrose- 


92 


MORPHOLOGY   OF   THE   CELL. 


very  soft  and  colorless.  Owing  to  their  yielding  character,  it  is 
not  easy  to  make  satisfactory  sections  for  their  demonstration, 
from  fresh  material ;  it  is  better 
to  keep  the  material  in  alcohol 
for  a  while,  or  to  dry  it  care- 
fully, as  Russow  advises.  All 
sections,  to  show  the  sieve-cells, 


must  be  very  thin.     The  following  measurements  of  single  large 
cells  given  by  de  Bary  serve  to  indicate  their  wide  range  in  size  : 


Cucurbita  Pepo  .  . 
Calamus  Rotang  .  . 
Potamogeton  natans 
Vitis  vinifera  . 


Length,  mm. 

.370 -.450    . 
2.000 

.275 


Transverse  diameter, 
.     .     .045 
.     .     .080 -.050 
.025 


281.   The  sieve-plates  occur  at  the  points  of  contact  of  sieve- 
cells.     They  are  always  found  at  the  ends  of  the  cells,  and  may 


cells  isolated  by  maceration ;  tlie  septa  are  in  their  winter  state.  7J,  branching  of 
cribrose-cell  isolated  by  maceration.  ( ',  tangential  section  across  a  medullary  ray, show- 
ing the  transverse  anastomosis  of  cribrose-cells ;  the  callus  at  the  septa  is  in  it*  winter 
state.  (Wilhelm.) 

FIG.  72.  Cribrose-cells  in  Vitis  vinifera.  Longitudinal  tangential  section  (beginning 
of  July)  through  the  bast  of  a  stem  t  cm.  thick ,  «/,  cribrose-cells,  the  oblique  as  well  as 
one  horizontal  perforated  septum  cut  longitudinally.  The  face  of  one  septum,  Imwi-ver, 
i*  slmwn  at  the  upper  part  of  the  figure;  rm,  medullary  rays.  (De  Bary.) 

FIG.  73.  Cucurbita  Pepo  Longitudinal  section  showing  terminal  sieve-plates  .it 
q,  <j,  and  a  lateral  one  at  si ;  ps,  contracted  protoplasm.  (Sachs. ) 


SIEVE-PLATES. 


93 


likewise  appear  upon  the  lateral  walls.  When  the  terminal  par- 
titions are  horizontal,  or  nearly  so,  they  are  cross-plates,  the 
whole  partition  forming  one  plate  ;  but  on  very  oblique  ends  the 
plates  may  be  separated  and  lie  in  one  or  more  rows.  The  plates  on 
the  walls  are  smaller  and  irregularly  distributed.  On  parts  of  the 
wall  contiguous  to  cells  of  any  other  kind  there 
may  be  dots ;  there  is  yet  some  doubt  as  to 
whether  they  are  perforations. 

The  diameter  of  the  sieve-pores  is  given  by 
Mohl  as  not  far  from  2  /x ;  but  although  some 
are  even  5  /x  in  diameter,  the  former  figure  is 
too  high  for  the  average. 

282.  That  which 
is  characteristic 
of  sieve-plates,  in 
distinction  from 
groups  of  perfo- 
rations elsewhere 
found,  is  a  thick- 
ening mass,  of 
bluish  lustre  and 
apparently  homo- 
geneous struc- 
ture, known  tech- 
nically as  the 
callus.  It  is  best 
shown  at  the  ter- 
minal plates,  es- 
pecially after  the 
application  of  a 
solution  of  iodine 
which  turns  it 
yellow,  and  makes 
it  more  sharply  defined.  In  concentrated  sulphuric  acid  and  in 
the  strong  alkalies  this  mass  swells  up  so  as  to  be  several  times 
its  original  size ;  and  in  the  former  it  soon  dissolves,  leaving 
only  slender  threads  in  its  place.  The  character  of  the  callus 


FIG.  74.  Finns  sylvestris.  Transverse  section  across  four  entirely  passive  tubes, 
which  are  somewhat  compressed  laterally,  uf  *.  (Janczewski.) 

FK;.  75.  Pinus  sylveKtri*.  Terminal  partition.  A  tube  inserted  upon  the  radial 
wall.  The  pores  of  the  terminal  partition  are  filled  with  warty  callus,  in  the  midst  of 
which  the  cellulose  network  may  always  be  seen;  in  the  pore  of  the  radial  wall  the 
Callus  is  completely  biuooth  aiid  round.  Tangential  section.  ^^.  (Janczewski.) 


94  MORPHOLOGY   OF   THE    CELL. 

varies  with  the  age  of  the   cell  and  with  the  time  of  year,  as 
shown  in  the  figures. 

283.  Anilin  blue  is  the  best  pigment  for  bringing  out  the 
form  of  the  callus  clearly.     If,  as  Russow l  recommends,  its  use 
be  supplemented  by  that  of  Schulze's  iodide,  the  callus  may  be 
seen  to  be  made  up  of  at  least  two  portions,  distinguished  by 
the  depth  of  color.     In  young  and  active  cribrose-cells  the  callus 
usually  appears  to  be  a  gelatinous  layer  on  each  side  of  the  sieve- 
plate  ;  in  most  old  cells  it  is  no  longer  seen. 

284.  Contents  of  the  cells.     In  the  younger  and  active  state 
just  referred  to,  the  cells  contain  a  wateiy  liquid  which  holds 
more  or  less  granular  matter,  and  the  walls  are  lined  by  a  delicate 
film  of  protoplasmic  substance.     That  the  callus  is  also  of  a  pro- 
toplasmic nature  is  not  clear,  although  some  of  its  reactions 
suggest  this.     It  frequently  contains  minute  granules  of  starch, 
which  sometimes  give  a  bluish-brown    color   with   iodine,  like 
starch  which  has  been  acted  on  by  diastase.    Russow  thinks  that 
a  ferment  is  present  in  the  cells  in  their  active  state.     When 
old,  most  cells  lose  not  only  the  callus  but  also  the  greater  part 
of  their  other  contents.      In  active  cells  there  are   frequentlj* 
found  very  small  but  brilliant  globules  which  are  albuminoidal. 
All  the  contents  above  mentioned  vary  within  certain  limits  at 
different  periods  of  the  year. 

285.  The   sieve-cells  of  the    higher   cryptogams   have   been 
shown  by  Janczewski 2  to  be  nearly  if  not  quite  imperforate  at 
all  seasons.     In  gymnosperms,  they  pass  through  two  periods : 
the  first,  or  the  evolutive,  in  which  the  plates  produce  the  callus, 
the  cells  themselves  containing  parietal  protoplasm  ;  the  second, 
or  passive,  stage,  in  which  the  protoplasm  disappears  entirely, 
and  communication  between  the  contiguous  cells  occurs.      In 
monocotyledons  and  dicotyledons  the  cells  have  four  periods; 
namely,  the  evolutive,  the  active,  the  transitory,  and  the  passive. 

IV.    Latex-cells,  Latex-tubes. 

286.  Certain  plants  when  wounded  exude  a  milky  juice  known 
as  latex.    They  belong  to  widely  separated  orders  ;  for  instance, 
to  Papaveraceoe,  Campanulaceae,  Asclepiadacese,  Urticace®,  etc. 

The  cells  in  which  latex  occurs  are  characterized  by  a  soft- 
ness of  cell-wall  which  renders  them  easily  compressible  ;  hence, 

1  Annales  des  Sc.  nat,  bot.,  se>.  6,  tome  xiv.,  p.  167. 
8  Annales  des  Sc.  nat.  bot,,  ser.  6,  tome  xiv.,  p.  50. 


LATEX-CELLS. 


95 


bounded  by  turgescent 
tissues,  their  contents 
readily  escape  through 
any  incision. 

Latex-cells  are  not 
restricted  to  any  one 
organ  of  the  plant,  but 
may,  and  generally  do, 
occur  in  all  parts,  and 
may  be  associated  with 
more  than  one  tissue- 
system.  They  are,  how- 
ever, usually  found  in 
parenchyma,  and  run  in 
the  same  general  direc- 
tion as  the  fibro-vascular 
bundles  near  which  they 
lie.  For  convenience,  they  ma} 


be  divided  into  the  simple  and 

b  the  complex. 

287.  The  simple 
forms  are  single 
cells,  which  may  be 
much  and  variously 
branched.  Subse- 
quent to  the  devel- 
opment of  one  of 
these  cells  in  a  plant, 
and  when  it  has  ex- 
tended its  ramifica- 
tions throughout  the 
different  organs,  a 
new  cell  may  inde- 
pendently give  rise  to 
new  branchings,  and 
to  a  new  system,  some 
of  the  branches  of 
the  two  cells  perhaps 
becoming  confluent. 
Good  examples  of  the 
simple  forms  are  af- 


Fm.  76.    Longitudinal  section  through  a  sepal  of  Chelidonium  majus,  showing  latex. 

"FIG.  77.  eLatex-tnbos  composed  of  confluent  cells:  «,  in  the  root;  b,  in  the  stem  of 
Chelidonium  majus.    (De  Bary.) 


§6  MORPHOLOGY  OS*   THE   CELL. 

forded  by  the  following  orders,  —  Asclepiadaceae,  Apocynaceae, 
and  Euphorbiaceae. 

The  complex  forms  consist  of  rows  of  cells  which  coalesce  to 
form  a  latex-system.  The  individual  cells  may  have  their  parti- 
tion-walls broken  down  very  early,  a  mere  vestige  of  them  remain- 
ing ;  or  the  partitions  may  be  simply  perforated,  so  as  to  allow  a 
free  communication  between  contiguous  cells.  Moreover,  the 
confluent  cells  may  be  conjoined  laterally,  thus  constituting  a 
complicated  network  which  runs  through  the  plant. 

288.  Occasionally  roundish  groups  of  perforations  resembling 
in  a  few  particulars  those  of  sieve-plates  are  found  in  the  latex- 
cells  of  Papaver  and  some  Cichoraceae  ;  but  they  are  coarser  and 
more  irregular,  and  are  devoid  of  the  peculiar  sieve-plate  struc- 
ture.    Moreover,  no  true  intermediate  forms  have  been  proved 
to  exist  between  the  two  kinds.1 

289.  The  wall  of  a  latex-cell  is  often  very  thin,  and  free  from 
any  markings  ;  but  with  even  slight  increase  of  thickness,  stria- 
tions  and  stratification  make  their  appearance,  projections  may 
extend  into  the  cavity  of  the  cell,  or  even  spirals  may  be  present. 
In  character,  the  cell-wall  possesses  many  of  the  peculiarities  of 
collcnchyma,  especially  in  its  behavior  with  iodine. 

290.  That  the  cells  contain  a  protoplasmic  lining  is  highly 
probable,  but  this  has  not  yet  been  satisfactorily  demonstrated. 
The  liquid  in  the  cells  consists  of  granular  matters  suspended  in 
a  watery  fluid,  and  imparting  to  it  a  milky  appearance.     Often 
the  color  of  the  liquid  is  yellow,  as  in  Argemone,  or  orange,  as  in 
Chelidonium.   The  watery  fluid  contains  in  solution  sugar,  gums, 
resins,  traces  of  albuminoid  matters,  and  various  principles,  for 
instance,  alkaloids  (like  morphia),  and  organic  acids. 

The  suspended  matters  are  of  minute  size,  with  the  excep- 
tion of  peculiar  forms  of  starch-granules.  When  perforation 
is  made  in  the  latex-system  of  a  turgescent  stem,  these  granules 
can  be  seen  to  move  towards  the  point  of  injury.  The  same 
movement  can  be  observed  when  the  pressure  on  one  part  of 
the  stem  is  materially  increased  ;  and  hence  arose  the  erroneous 
belief  that  there  is  a  circulation  of  latex.2 

291.  Upon  exposure  to  the  air  latex  coagulates,  and  forms 
upon  drying  a  sticky,  elastic  mass,  which  in  some  plants  is  suffi- 
ciently abundant  to  furnish  the  india-rubber  of  commerce. 

1  D.  H.   Scott :   On  the   development  of  articulated   laticiferous  vessels. 
Journ.  Mic.  Science,  1882,  p.  144.     An  interesting  account  is  also  given  by 
de  Bary,  from  notes  by  Schmalhausen,  Vergleichende  Anatomic,  p.  205. 

2  Schultz  :  Die  Cyklose  des  Lebenssaftes  in  den  Pflaiizen,  1841,  p.  282. 


IBIOBLASTS.  97 

RECEPTACLES  FOR  SECRETIONS. 

292.  Individual  cells  (idioblasts)  may  differ  greatly  from  their 
neighbors  as  respects  their  contents.     Such  cells  may  be  well 
named  after  their  characteristic  contents  ;  as  crystal-cells,  resin- 
cells,  mucilage-cells,  tannin-cells,  etc. 

293.  Thej-  vary  much  in  shape  and  size.     Frequently  they  are 
not  readily  distinguishable  from  their  immediate  neighbors  by 
anything  except  their  contents.     In  other  cases,  however,  they 
may  assume  forms  widely  different  from  those  of  the  cells  around 
them,  and  may  also  be  distinguished  b\*  their  size.     They  are 
often  so  associated  together  as  to  form  "  glands." 

294.  Crystal-cells.     These  sometimes,  as  de  Bary  points  out, 
curiously  resemble  the  shape  of  the  crystal  or  groups  of  crystals 


which  they  contain.  Thus  globular  clusters  are  generally  con- 
tained in  spherical  cells,  elongated  prisms  in  elongated  cells 
(as  in  Quillaja).  "In  man}-  trees  each  cambium-cell  (as  it 
develops  into  a  bast-fibre)  may  be  divided  by  diagonal  partitions 
into  numerous  (20  to  30)  chambers,  the  height  of  which  is  about 
the  same  as  the  width,  and  each  is  filled  by  a  cnrstal  or  a  small 
cluster.  In  this  case  the  general  outline  of  the  original  cambium- 
cell  remains  unaltered,  and  the  whole  row  of  compartments  may 
be  isolated  as  a  chambered  fibre."1  The  bast-cells  containing 
crystals  have  been  already  noticed. 

295.  Resin-cells.  In  a  large  number  of  plants  soft  viscid 
substances  are  present,  which  exude  when  the  tissues  are 
wounded.  They  may  be  roughh'  classed  into  (1)  Balsams,  in 
which  resinous  matter  is  mixed  with  a  considerable  proportion  of 

1  De  Bary  :  Vergleichende  Anatomic,  p.  145. 

PIG.  "8.  Crystal-cells :  a,  from  the  petiole  of  Begonia  mauicata;  b,  a  cell  with  raph- 
Ides,  from  Lemna  trisulca;  c,  from  Phallus  caninus.  (Kny.) 

7 


98 


MORPHOLOGY   OF   THE   CELL. 


one  or  more  essential  oils,  forming  a  thickish  liquid  ;  (2)  JResins, 
which  have  comparatively  little  essential  oil  commingled,  and  are 
of  various  grades  of  hardness  ;  (3)  Gum-resins,  or  resins  hav- 
ing more  or  less  mucilaginous  or  gummy  matters.  To  the  lattei 
class  are  sometimes  referred 
the  products  left  by  the  drying 


of  many  milky  juices  (latex)  ;  of  such,  caoutchouc  is  an  ex- 
ample. All  the  foregoing  substances  may  be  found  in  single 
cells,  which  are  of  ver}-  diverse  forms. 

296.  Roundish  cells  of  this  character  are  found  in  the  Mag- 
noliaceae  and  some  Composite,  etc.  Long  cells  are  to  be  de- 
tected in  some  Liliaceae,  etc.,  and  they  are  connected  b}*  many 
intermediate  forms  with  resin-ducts  arising  from  the  confluence 
of  several  cells.  On  the  other  hand,  they  pass  by  various  gra- 
dations into  structures  which  are  generally  referred  to  the  latex- 

FIG.  79.  Transverse  section  through  the  leaf  of  Psoralea  hirta ;  the  epidermis  con- 
sisting of  one  layer  with  some  of  the  tissue  shown  on  both  sides  of  the  glnnd:  A,  very 
young  state  in  which  the  secretion  is  not  yet  present;  B,  somewhat  older,  secretion 
commencing;  C,  mature  state.  (Dc  Bary.) 

FIG.  80.  A  "  gland"  in  Dictamnns  Fraxinella  :  A,  K,  early  stages;  C,  mature  itate; 
p,p,  c,  mother-cells  of  the  gland-tissue;  i?,  the  covering  layer  forming  a  continuation  of 
the  epidermis ;  o,  a  large  drop  of  oil  (Hauler . ) 


INTERCELLULAR   SPACES. 


99 


system.  To  this  system  should  perhaps  be  referred  also  numer- 
ous cases  of  pigment-cells,  like  those  in  the  roots  of  madder  and 
rhubarb ;  also  the  peculiar  bodies  seen  in  the  periphery  of  the 
pith  of  Sambucus,  and  the  milk-sacs  of  some  species  of  Acer. 

297.  Mucilage-cells  are  larger  than  the  surrounding  cells,  and 
sometimes  closely  resemble  intercellular  spaces  filled  with  muci- 
laginous matter.     In  some  instances  the  mucilage  is  distinctly 
referable  to  changes  in  the  contents  of  the  cell,  in  others  to  a 
disorganization   of  a  portion  of  the  wall,   while  in  still  others 
both  sources  may  be  recognized.1 

298.  Cells  containing   tannin  in  very  large  amount  are  fre- 
quently met  with,  but  they  do  not  call  for  special  remark. 

299.  Resins  and  the  like  are  found  not  only  in  single  cells 
but  also  in  spaces  formed  by  the  breaking  down  of  the  interven- 
ing walls  of  cell-clusters  of  various  shapes ;  hence  various  forms 
of  receptacles  for  these  substances  may  be  looked  for. 

INTERCELLULAR  SPACES. 

300.  The  walls  of  cells  still  capable  of  division  are  generally  in 
unbroken  contact ;  but  as  differentiation  goes  on  they  may  be- 
come separated  more  or 

less  by  unequal  growth 
or  by  a  breaking  down 
of  intermediate  cells.2 
The  intercellular  spaces 
thus  formed  may  be  mere 
chinks,  or  they  may  be- 
come chambers  of  large 
size.  They  may  con- 
tain merely  air,  or  air 
and  water}-  sap,  or  most 
of  the  matters  described 
in  the  previous  sections. 
Air-spaces  in  the 
looser  tissues  of  plants 
are  general^  so  con-  8l 

1  The  details  of  this  subject  can  be  found  in  Prings.  Jahrb.,  v.  161  (Frank), 
and  Annales  des  Sc.  nat.,  ser.  6,  tome  i.  p.  176  (Prillieux). 

8  The  first  mode  of  development  of  intercellular  spaces  has  been  termed 
schizogenic,  the  latter  lytiycnic  ;  moreover,  a  distinction  may  be  made  between 
those  intercellular  spaces  which  are  formed  when  the  tissues  begin  to  differen- 
tiate, —  protoiiciifi;  —  and  tho-e  formed  in  older  tissues,  —  hysteroyenic. 

FIG.  81.  Transverse  section  through  th«  stem  of  Etatiue  Aisiuastrum,  showing  large 
intercellular  spaces.  /(,  containing  ;ur.  (Reinke.) 


100  MORPHOLOGY   OF   THE   CELL. 

nected  throughout  the  plant,  and  communicate  so  directly  with 
the  stomata,  that  they  constitute  an  apparatus  for  bringing  the 
interior  of  the  structure  into  close  relations  with  the  outer  air. 
Sometimes  the  aggregate  volume  of  the  air-spaces  is  very  large 
in  proportion  to  the  volume  occupied  by  the  cells  themselves.1 

In  composition,  the  air  within  the  plant  usualty  differs  from 
that  of  the  atmosphere  in  containing  a  larger  proportion  of 
nitrogen.  If  the  air-spaces  are  much  smaller  than  the  cells 
which  surround  them,  they  are  termed  interstices ;  if  about  as 
large  as  the  colls,  lacunae  ;  if  conspicuously  larger,  air-passages 
or  air-chambers.  Two  chief  forms  of  lacunae  are  distinguished 
by  de  Bary ;  namely,  cavities  surrounded  by  cells  which  are 
more  or  less  branched,  and  those  surrounded  by  plates  of  cells. 
Good  examples  of  the  former  are  afforded  by  many  water-plants, 
rushes  and  the  like  ;  of  the  latter,  by  the  stems  of  man3T  Araceae, 
for  instance,  Acorus  Calamus. 

301.  The  continuity  of  the  larger  air-passages  may  be  inter- 
rupted by  plates  crossing  at  an  angle  (generally  slightly  oblique). 
Such  dividing  plates,  termed  diaphragms,  are  frequently  com- 
plicated in  their  structure. 

302.  Hairs,  sometimes  much  branched,  are  found  in  the  larger 
air-passages  of  many  plants.     These  form  the  stellate  structures 
in  the  N3-mpha?acea?,  and  the  "  H-like"  cells  in  some  Araceae. 

303.  Intercellular  spaces,  usually  those  of  small  size,  may 
contain  water  together  with  air.     This  is  the  case  in  the  cavities 
under  the  water-pores  of  Fuchsia,  etc. 

304.  When  intercellular  spaces  contain  resins,  oils,  and  the 
like,  they  constitute,  together  with  the  simple  cells  described  in 
295,  the  structures  loosely  called  internal  glands.     Often  these 
are  merely  irregular  spaces  left  by  the  breaking  down  of  one  or 

1  The  following  measurements  are  taken  from  Unger  (Sitzungsb.  d.  Wiener 
Akad.,  xii.  373). 


Name  of  plant. 

Parts  examined. 

No.  of  parts 
by  volume  of  air 
in  1000  parts 
of  the  plant. 

Paspalurn  setaceum. 
Musa  sapient  urn. 
Nlcotiana  Tahacum. 
Brassica  Rapa. 
Begonia  manicata. 
Camellia  Japnnira. 
Prniius  Lanroceranu. 
Aocnha  Japonloa. 
Ardisia  crenulata. 

Four  leaves  with  their  sheaths. 
Piece  of  the  leaf-stalk. 
Leaf  with  leaf-stalk. 
I,eaf  with  leaf-stalk. 
One  leaf  with  its  stalk. 
Two  leaves  with  their  stalks. 
One  leaf  with  its  stalk. 
One  leaf  with  it*  stalk. 
Four  leaves  with  short  stalks. 

68 
480 
256 
175 
66 
224 
219 
273 
220 

RESIN-PASSAGES. 


101 


more  cells,  but  they  sometimes  have  a  remarkable  regularity  ol 
form  and  clearness  of  outline. 

It  has  been  observed  that  these  spaces  filled  with  resinous  and 
other  matters  are  not,  as  a  rule,  met  with  in  the  plants  which  are 
provided  with  the  simpler  receptacles,  consisting  of  single  cells 
or  small  groups.  De  Bary  classifies  these  resin-passages  and 


spaces  as  follows:  (1)  those  passages  which  contain  mucilage 
and  gums,  as  those  in  the  Cycads,  species  of  Canna,  Opuntia, 
and  some  Araliaceae ;  (2)  resin-canals  and  cavities  containing 
resins,  ethereal  oils,  emulsions  of  resinous  gums,  etc.,  variable  in 
quality  in  different  cases ;  a,  passages  or  canals,  as  those  in 
Coniferae,  Alismaccst,  Aroideae,  the  tubuli-flowered  Coinpositae, 
IT  m  belli  ferae,  Araliaceae,  Anacardiaceae  ;  6,  short  cavities,  as  in 
species  of  Hypericum  and  the  true  Rutaceae,  many  species  of 
Oxalis  and  Myrtaceae,  and  some  species  of  Lysimachia.  The 
cells  which  surround  the  more  complete  cavities  are  so  different 
from  the  neighboring  parenchyma  that  they  have  been  termed, 
collectivel}",  the  epithelium  of  the  spaces. 

It  is  not  fully  known  in  what  way  the  various  resinous  and 
mucilaginous  matters  are  produced  in  the  cavities.  In  some 
instances,  at  least,  the  matters  appear  at  a  very  early  stage  of 
the  development  of  the  cells  which  are  afterwards  broken  down 
to  form  the  cavity.  The  special  cases,  like  those  of  the  Myrta- 
ceae, in  which  the  cavities  contain  oil,  are  best  for  purposes  of 
study,  because  they  are  so  frequently  to  be  found  in  the  thinnest 
leaves,  and  at  an  early  stage  of  development. 

PIG.  82.  Transverse  section  of  part  of  leaf  of  Pinus  Lariclo.  showing  a  resin-passage, 
HC.  (Kny.) 


CHAPTER  III. 

MINUTE    STRUCTURE    AND    DEVELOPMENT    OF    THE   ROOT, 
STEM,   AND   LEAF   OF  PH.ENOGAMOUS   PLANTS. 

GENERAL   CONSIDERATIONS. 

305.  THE  tissue  elements,  described  in  the  preceding  chapter, 
are  arranged  in  various  ways  to  form  and  connect  the  organs  of 
the  plant.     If  elements  of  the  same  kind  are  united,  they  consti- 
tute a  tissue,  to  which  is  given  the  name  of  those  elements  ;  thus 
parenchyma  cells  form  parenchyma  tissue  or  simply  parenchyma  ; 
cork-cells  form  cork,  etc.     A  tissue  can  therefore  he  defined  as 
a  fabric  of  united  cells  which  have  had  a  common  origin  and 
have  obeyed  a  common  law  of  growth. 

Tissues  are  united  to  form  systems;  systems,  to  form' organs. 

306.  In  nearly  all  plants  with  which  the  present  treatise  deals 
there  is  some  kind  of  framework  consisting  mainly  of  the  more 
elongated  cells  and  ducts.     This   framework   runs   throughout 
the  entire  organism.     It  is  surrounded  by  parenchyma,  in  which 
other  tissue  elements  may  also  occur ;  the  epidermis  in  some  of 
its  modifications  covers  the  whole. 

307.  The  three  chief  systems  found  in  plants  are,  therefore, 
the  fascicular,  the  cellular,  and  the  epidermal ;  and  these  corre- 
spond in  a  general  way  to  three  classes  of  functions.     In  the 
cellular  system  are  found  the  active  cells  by  which  assimilation, 
the  proper  work  of  the  plant,  is  effected  ;  the  fascicular  system  is 
largely  conductive,  and  serves  also  important  mechanical  ends ; 
the  epidermal  system  brings  the  assimilative  apparatus  of  the 
plant  into  safe  relations  with  the  surroundings. 

No  discussion  of  the  cellular  and  epidermal  systems,  intro- 
ductory to  a  special  consideration  of  them  as  they  occur  in  the 
different  organs,  is  needed ;  but  some  general  statements  relative 
to  the  fascicular  system  will  obviate  repetitions  later. 

308.  The  fascicular  system,  in  its  most  complete  development, 
comprises  the  following  tissue  elements,  which  occur  in  very 
different  proportions  in  different  cases,  —  prosenchyma  in  the 
widest  sense,  including  wood-cells  of  all  kinds,  ducts,  fibres,  and 
cribrose-cells;  together  with  some  commingled  parenchyma.  With 


FIBRO-VASCULAR    BUNDLES. 


103 


the  exception  of  the  parenchyma,  all  these  elements  are  elongated 
and  are  arranged  in  various  sorts  of  fascicles  or  bundles,  whence 
the  name,  the  fascicular  system.  Since  fibres  and  vessels  play 
such  an  important  part  in  the  composition  of  this  system,  it  has 
been  also  called  the  fibro- vascular  system,  and  the  bundles,  fibro- 
vascular  bundles. 

309.  When  reduced  to  its  lowest  terms,  a  fibro-vascular  bun- 
dle consists  of  two  tissue  elements,  namely,  cribrose-cells  and 
tracheal  cells,  the  latter  being  sometimes  replaced  either  wholly 
or  in  part  by  ducts. 

310.  The  two   elements   are    usually   associated    with   some 
parenchyma  and  with  a  considerable  proportion  of  long  bast- 


fibres  ;  but,  while  preserving  a  general  uniformity  of  structure 
throughout,  a  bundle  ma}-  become  considerably  changed  in  com- 
position during  its  course.  This  is  well  shown  by  comparing 
sections  taken  at  some  distance  from  each  other ;  for  instance, 


FIG.  83.  Longitudinal  radial  section  of  a  collateral  fibro-vascular  bundle,  from  the 
stem  of  a  dicotyledon  :  b— i,  wood;  i—n,  liber;  the  wood  comprises,  b,  a  narrow  annular 
duct,  c,  wider  spiral  duct,  rf,  a.  duct  with  septum,  e,  woody  parenchyma,  /,  woody  fibre, 
g,  wide  duct  with  areolated  pits,  h,  septate  woody  fibres;  the  liber  comprises,  n,  liber- 
fibres,  m,  short  parenchyma,  /,  cribrose-cells,  i,  cambium,  A%  long  parenchyma  or  0:1111- 
biform.  (Kny.) 


104  MINUTE   STRUCTURE   OF   ORGANS. 

one  made  in  the  middle  of  the  course  of  a  bundle  with  one  near 
its  extremity. 

311.  The  cribrose  part  of  the  bundle  may  also  be  termed  its 
liber-portion  or  bast-portion  ;  the  tracheal,  its  woody  portion. 
These  terms  are  not  liable  to  be  confounded  with  any  others, 
since  it  is  with  the  cribrose  portion  that  the  well-known  bast- 
fibres  or  liber-fibres  are  associated,  while  it  is  in  the  tracheal 
portion  that  all  the  constituents  of  wood  are  found. 

312.  For  the  first  term  (bast-portion),  Nageli  has  introduced 
the  word  Phloem  ;  for  the  second  (wood-portion),  Xylem.     In 
this  treatise  these  terms  will  be  used  interchangeably  with  the 
others.     But  the  woody  portion  of  a  bundle  is  sometimes  very 
far  from  being  conspicuously  lignified,  and  the  bast-portion  may 
be  much  reduced. 

313.  The  three  principal  ways  in  which  the  elements  of  bun- 
dles are  arranged  are :    1.  A  single  strand  of  liber  has  one  side 
in  contact  with  a  single  strand  of  wood,  the  two  running  side  by 
side.  —  the  collateral  bundle.    This  mode  of  arrangement  is  com- 
mon in  the  stems  of  phrenogams.     A  variet}*  of  the  collateral 
bundle  has  a  strand  of  liber  on  each  side  of  the  wood,  or,  con- 
versely, a  strand  of  wood  on  each  side  of  the  liber,  —  the  bicollat- 
eral  bundle.     2.  The  strands  of  liber  and  wood  are  in  different 
radii,  —  the  radial  bundle.     This  is  the  most  common  mode  of 
arrangement  in  roots.     3.  A  strand  of  one  element  is  wholly  en- 
veloped by  the  other  element, — the  concentric  bundle.     These 
modes  of  arrangement  will  be  further  discussed  under  "  Roots  " 
and  ••  Stems." 

314.  The  bundles  are  surrounded  by  parenchyma  ;  but  this  is 
very  frequently  limited  at  the  periphery  of  the  bundle  by  a  cylin- 
der formed  of  closely  united  parenchyma  cells,  which  contain 
considerable  starch.     The  endodermis  is  a  special  case  of  this 
structure,  in  which  the  cells  are  more  or  less  distinctly  cutini/rd. 
When  this  enveloping  cylinder  is  well  defined,  it  is  known  as  the 
bundle-sheath.1 

315.  At  first,  each  bundle  consists  of  similar  cells  (procam- 
bium),  some   of  which   differentiate   into   fibres,   vessels,  etc. 
Bundles  in  which  all  the  procambium  cells  become  permanent 
cells  are  closed;  those  which  retain  an  inner  portion  (cambium) 
capable  of  further  differentiation  are  open. 


TUC- 


1  Iii  a  great  number  of  instances  it  is  convenient  to  refer  to  the  same  st.«v- 
ture  the  long  and  firm  bast-cells  which  are  found  at  one  side  of  the  bundle  ; 
but  the  subject,  when  examined  from  the  j>oint  of  view  of  development,  espe- 
cially when  the  vascular  cryptogams  are.  taken  into  account,  presents  so  many 
difficulties  that  it  may  be  here  left  without  further  treatment. 


MERISTEM. 


105 


316.  As  regards  the  course  of  the  bundles  through  the  plant, 
it  is  sufficient  to  note  here  that  they  are  variously  combined  in  the 
different  organs,  sometimes  forming  compact  masses  of  tissues, 
and  at  others  running  as  slender  and  delicate  isolated  threads. 

317.  It  has  been  seen  in  201  that  ineristem  is  the  nascent 
state  of  any  tissue,  and  that  it  may  multiply  as  such,  or  first 
become  differentiated 

into  elongated  forms 
(cambium).  For  con- 
venience of  reference, 
the  meristem  at  the 
growing-points  of  the 
axis  of  the  plant  is 
given  special  names : 
Dermatogen,  the 
layer  of  nascent  epi- 
dermis ;  Periblem, 
the  layer  of  nascent  cortex  just  beneath  the  epidermis  ;  Plerom,, 
the  cylinder  or  shaft  of  nascent  fascicles.  The  cells  from  which 
these  primordial  layers  or  masses  of  nascent  tissues  arise  are 
known  as  initial  cells.1 

The  initial  cells  produce  primordial  layers  or  masses  of  tissues  ; 
by  their  further  development  the  primordial  layers  or  masses 
give  rise  to  the  early  distinctive  tissues  of  an  organ.  The  tis- 
sues thus  early  formed  constitute  the  primary  structure  of  the 
plant. 

318.  In  the  further  growth  of  an  organ,  especially  in  plants 
which  are  to  live  more  than  a  single  year,  or  which  have  a  well- 
defined  period  of  rest,  remarkable  changes  may  take  place  in  its 
structure,  especially  by  the  introduction  of  new  elements.     Such 
changes  are  known  as  secondary,  and  give  rise  to  the  secondary 
structure  of  the  organ.     From  the  nature  of  the  case,  it  is  im- 
possible to  draw  a  sharp  line  between  the  primary  and  secondary 
structure  ;  but  the  division  is  nevertheless  useful  in  the  exami- 
nation of  the  minute  anatonn*  of  the  plant. 

1  Hanstein  :  Die  Scheitelzellgrupp*1  im  Vegetationspunkt  der  Phanerogamen, 
1868  ;  also  in  Botanische  Abhandlungen,  1871,  p.  3. 

The  distinction  between  meristem  proper  and  cambium  is  insisted  on  by 
Nageli  in  hi.s  Beitriigc  (1858). 

FIG.  84.  Longitudinal  section  through  the  middle  of  the  root-tip  of  the  embryo  of 
Pontederia  cordata.  The  lower  initial  cells  produce  the  cap.  c  ;  the  middle,  the  nascent 
cortex,  ec :  the  upper,  the  nascent  central  cylinder,  cc.  The  nascent  epidermis,  ep,  of 
the  stem  is  continued  down  to  the  cap ;  «,  the  point  to  which  the  suspensor  was  attached. 
In  other  terms,  cc  is  the  plerom,  ec,  periblem,  ep,  deriuatogen.  (Flahault.) 


106 


MINUTE    STRUCTURE   OF   THE    ROOT. 


THE    ROOT. 
PRIMARY  STRUCTURE. 


OIllj 

differences  exist  between  these 
cells,  both  as  regards  shape 
and  size  ;  at  the  very  end  of  the 
radicle  the}-  are  relatively  large, 
and  form  a  sort  of  cap-like  cov- 
ering (root-cap]  for  the  smaller 
cells  lying  directly  back  (the 
growing-point).  If  the  section 
is  thin  enough,  it  will  be  seen 
that  at  the  growing-point  numer- 
ous rows  of  cells  appear  to  con- 
verge, the  fact  being  that  all  the 
cells  of  such  rows  are  derived  by 
multiplication  from  those  at  the 
growing-point. 

321.  Certain  differences  in  the 
arrangement  of  these  rows  can 
be  seen  upon  comparing  the  radi- 
cles of  plants  of  different  classes. 


319.  It  was  stated  in  Vol. 
I.,  p.  27,  that  the   root,   or 
descending  axis,  "•  normally 
begins  in  germination  at  the 
root-end  of  the  caulicle,  or 
so-called   radicle ;    but   that 
roots  soon  proceed,  or  may 
proceed,  from  other  parts  of 
the  stem,  when  this  is  favor- 
ably situated  for  their  pro- 
duction." 

320.  A  longitudinal   sec- 
tion  through   the   tip   of  a 
germinating  radicle  exhibits 

parenchyma   cells.      Slight 


FIG.  85.  Longitudinal  section  through  the  middle  of  the  root-tip  of  Fagopyrnm  escu- 
lentum.  The  lower  initial  cells  prive  rise  to  the  cap  c,  ami  the  epidermis  e'p ;  the  middle 
produce  the  cortex  c'e ;  ;><?,  peripheral  layer  of  the  central  cylinder  cc,  which  comes 
from  the  upper  initial  cell*.  (Janczewskl.) 

Fio.  86.  Longitudinal  section  through  the  middle  of  a  lateral  root  of  Pontederla 
crassipes:  cc,  nascent  central  cylinder  (plerom);  r'c,  nascent  cortex  (periblem);  e'p, 
nascent  epidermis  (dermatogen) ;  c,  root-cap.  (Flahaulfc.) 


THE    ROOT-CAP.  107 

Thus  in  most  cases  the  group  composing  the  point  of  growth 
consists  of  three  kinds  of  superposed  cells,  so  arranged  in  layers 
that  each  gives  rise  to  a  determinate  portion  of  the  forming 
root :  (1)  the  outer  or  lower  layer,  to  the  root-cap  and  the  rest  of 
the  epidermis;  (2)  the  middle,  to  the  cells  which  are  immediately 
under  the  epidermis,  —  the  cortex;  (3)  the  inner  or  upper  laver, 
to  the  central  cylinder.  But  in  some  plants  *  there  are  more 
than  three  Ia3'ers  of  initial  cells  (e.  g.,  Sparganium,  Raphanus, 
etc.)?  while  in  others  there  are  less  than  three  (e.  g.,  only  one  in 
Cucurbitaceae,  two  in  Triticum). 

322.  The  Root-cap.    The  growing-points  of  nascent  roots  origi- 
nate just  below  the  surface  of  the  organ  whence  they  proceed  ; 
hence  roots  are  said  to  be  formed  endogenously.     In  emerging, 
the)-  rupture  the  layer  of  tissue  by  which  they  had  been  covered, 
but  are  from  the  first  protected  at  the  end  by  a  thicker  or  thinner 
mass  of  parenchyma,  —  the  root-cap.2 

323.  It  does  not  always  have  the  same  origin,  as  will  be  seen 
by  the  notes,8  nor  has  it  the  same  shape  and  size  in  all  plants. 

1  Jauczewski  (Ann.  des  Sc.  nat.,  ser.  5,  tome  xx.,  1874)  describes  six  types 
of  development  of  the  tissues  of  the  root  :  — 

1.  Four  distinct  layers  of  meristem  ;  namely,  Plerom,  Periblem,  Dermato- 
gen,  and  Calyptrogen  ;  e.  g.,  Hydrocharis. 

2.  A  distinct  Plerom  and  Calyptrogeii,  but  the  Periblern  and  Dermatogen 
have  initial  cells  in  common  ;  e.  g.,  Graminece. 

3.  A  distinct  Plerom  ;   the  Periblem,  Dermatogen,  and  Calyptrogen  have 
common  initial  cells  ;  e.  g.,  Iridacece. 

4.  A  distinct  Plerom  and  Periblem  ;  the  Dermatogen  and  Calyptrogen  have 
common  initial  cells  ;  e.  g.,  Helianthus  animus. 

5.  All  four  layers  have  common  initial  cells  ;  e.  g.,  Phaseolns  and  Pisum. 

6.  Only  a  distinct  Plerom  and  Periblem  ;  therefore  there  is  neither  true 
epidermis  nor  root-cap,  since  these  are  formed  simply  by  outer  layers  of  the 
Periblem  ;  e.  g.,  GyinnospermoK. 

Treub  (1876)  and  Eriksson  (1878)  distinguish  seven  types. 

*  According  to  Olivier,  a  part  of  the  tissue  thus  broken  through  by  the 
advancing  radicle  of  grasses  remains  at  its  base,  as  the  coleorhiza,  while  the 
rest  becomes  the  root-cap  (Ann.  des  Sc.  nat.,  ser  6,  tome  xi.,  1881,  p.  19). 

8  According  to  Flahault  (Recherches  sur  I'accroissement  terminal  de  la  racine 
chez  les  Phanerogames,  Ann.  des  Sc.  nat.,  ser.  6,  tome  vi.,  1878),  who  bases  his 
opinion  on  an  examination  of  three  hundred  and  fifty  species  of  Phamogams, 
the  terminal  growth  of  the  root  may  be  referred  to  two  structural  types  which 
are  characteristic  of  monocotyledons  and  dicotyledons. 

In  monocotyledons  the  epidermis  is  generally  formed  by  the  initial  cells  of 
the  cortex.  The  epidermis  never  gives  rise  to  a  root-cap  ;  the  root-cap  once 
formed  is  continually  renewed  by  the  activity  of  its  internal  layers.  In  dicoty- 
ledons, on  the  other  hand,  the  epidermis  is  almost  ahvnys  independent  of  the 
cortex  ;  the  root-cap  is  continually  renewed  by  the  activity  of  the  cortex  and 
epidermis. 


108 


MINUTE   STiiUCTURE   OF   THE  HOOT. 


Roots  which  grow  in  the  earth  seldom  have  it  much  developed ; 
but  in  many  aquatics  it  becomes  of  large  size,  though  it  is  always 
thin.     In  some  species  of  Pontederia  the  cap  envelops  the  root 
for  the  length  of  half  a  centimeter ;  but  it  is  free 
at  its  upper  part,  and  is  in  contact  with  the  root 
only  at  its  very  tip.      The  roots  of  Typhaceae 
and  Lemnaceae   exhibit  nearly  the  same  struc- 
ture.    The  cap  consists  in  these  cases  of  only 
one  or  two  layers  of  thin-walled  cells. 

The  aerial  roots  of  some  plants  have  large 
root-caps  composed  of  firm -walled  cells.  This 
is  well  shown  in  Pandanus,  where  the  cap  con- 
sists of  many  layers  of  cutinized  cells.  The 
cap  in  all  cases  exfoliates  on  its  exterior,  and 
is  as  constantly  renewed  03-  the  cells  within. 
Nearly  all  of  its  cells  contain  starch-granules 
in  abundance. 

324.  The  peripheral  tissue  in  the  rootlet  does 
not  always  have  the  same  origin  ;  it  may  in  some 
cases  be  regarded  as  true  epidermis,  in  others  as 
the  outermost  portion  of  the  cortical  parenchyma.  In  the  vast 
majority  of  cases  this  young  superficial  tissue  is  furnished  with 
root-hairs  ;  it  is  therefore  designated  the  piliferous  layer.1 

325.  The  piliferous  layer  has  no  intercellular  spaces  (a  few 
cases  of  aerial  roots  of  Orchids  excepted).     The  hairs  are  con- 
fined to  a  narrow  zone  a  short  distance  behind  the  tip.  although 
in  Triglochiu  they  have   been  found  on  the  edges  of  the  cap, 
and  in  Philodendron   very  near  its  edge.      When  first  formed 
they  have  delicate  transparent  walls,  and  are  filled  with  pro- 
toplasm.    By  the  advance  of  the  growing-point  and  with  the 
formation  of  new  hairs,  the  older  become  less  active,  their  walls 
thicken  and  turn  brown,  their  contents  disappear,  and  they  fall 
off,  generally  leaving  a  nearly  glabrous  surface. 

326.  The  hairs  are  generally  simple,  but  in  the  adventitious 
roots  of  some  Bromeliaceae  2  compound  hairs  are  also  found. 

Branched  hairs  are  seen  on  the  roots  of  Saxifraga  sarmentosa, 
Brassica  Napus,  etc. 

1  Olivier  (Ann.  des  Sc.  nat.,  ser.  6,  tomexi.,  1881,  p.  19),  according  to  whom 
it  is  never  homologous  with  the  epidermis  of  the  stem  (p.  28). 

8  Jorgensen,  Botanisk  Tidsskrift,  1878,  p.  144. 

FIG.  87.    Seedling  of  Sinapis  alba,  showing  root-haire. 

FIG.  88.  Seedling  of  same,  showing  the  ni:mn,T  in  which  Hue  particle*  of  earth  cline 
to  the  root-hairs.  (Sachs.) 


ROOT-HAIRS. 


109 


327.  Root-hairs  are  best  obtained  for  study  by  cultivating 
seedlings  on  moist  glass,  or  with  the  rootlets  in  water.     It  is  well 
to  compare  the  forms  thus  obtained  with  those  found  on  roots  of 
the  same  plant  grown  in  loam,  sand,  fine  clay,  etc.     Masters  has 
shown  that   the   develop- 
ment of  the   hairs  is  fa- 
vored by  many  conditions, 

such  as  porosity  of  the 
soil,  moisture,  etc.  ;  and 
this  fact  should  be  borne 
in  mind  in  the  examina- 
tion of  the  root-hairs  of 
any  plant. 

328.  The  walls  of  root- 
hairs  are  only  slightly  cu- 
tinized,  but  there  is  a  great 
difference  in  this  respect 
in  different  plants. 

329.  The  cells  of  the 
superficial    layer    of    the 
rootlet,  other  than   those 
with  hairs,   are    more   or 
less  cutinized,  the  degree 
of   infiltration   depending 
upon  their  age.     In  some 

cases  (e.  g.,  Asphodelus)  the  thickening  is  very  considerable. 

330.  On  a  few  plants1  no  root-hairs  have  been  detected,  as 
Crocus  sativus,  Cicuta  virosa,  Abies  pectinata  and  many  other 
gymnosperms. 

331.  Roots  of  orchids.     The  newer  parts  of  the  aerial  roots 
of  Orchids  have  an  epidermis   consisting  of  nearly  spherical 
tracheids,  which,  except  sometimes  in  the  outermost  Ia3'ers,  co- 
here without  intercellular  spaces.     The  walls  of  these  cells  are 
colorless,  though  in  mass  the}-  may  have  a  silvery  lustre,  and 
when  immersed  in  water  they  soon  become  sufficiently  trans- 
parent to  permit  the  subjacent  green  tissue  to  be  seen.2 

1  Duchartre  (Elements  de  Botanique,  1867,  p.  214)  cites  other  plants. 

See  also  a  valuable  paper  by  Schwarz  in  Untersuchungen  aus  dem  bot. 
Inst.,  Tubingen,  1882. 

2  According  to  Leitgeb,  the  old  roots  of  Vanda  furva  are  green  because  their 
tracheids  contain  minute  Algae  (De  Bary,  Vergl.  Anat.,  p.  238). 

Fm  89.  Root-hairs  distorted  by  contact  with  the  soil.  Fourin  therigM-hand  nj>ppr 
corner,  Selaginella;  three  in  lower  corner,  Trifolium  ;  the  others,  Avena.  The  dark 
points  indicate  the  attached  particle  of  soil,  a,  a,  a,  minute  prolongations  of  the  cell- 
wall.  (Sachs.1) 


110  MINUTE   STRUCTURE   OF   THE   KOOT. 

332.  Sometimes  there  are  papillar  outgrowths  from  these  tra- 
chei'ds,  which  are  to  be  regarded  as  root-hairs.      They  occur 
chiefly  on  younger  parts  of  the  roots  which  are  in  contact  with 
a  moist  support,  or  which  are  kept  wet.     They  cling  tenaciously 
to  moist  surfaces,  and  may  become  much  widened  and  flattened.1 

333.  The  cortex  of  different  plants  varies  greatly  in  thickness 
and  compactness,   and  in  the  thickness  of  the  cell-walls.      In 


90 

a  few  cases  remarkable  lacunre  are  to  be  seen   (e.  g.,  Meny- 
anthes). 

334.  The  cells  bounding  the  inner  layer  of  the  cortex  have  the 
general  characters  described  under  "  Endodermis  ;"  their  radial 
walls  are  generally  more  or  less  plicate,  and  there  are  no  inter- 
cellular spaces. 

335.  In  the  primary  cortex  of  roots  all  the  various  kinds 
of  secreting  cells  and  receptacles  for  exudations  described  on 
p.  97  may  be  looked  for ;  but  as  a  rule  they  are  less  developed 
than  in  the  stem.      Collenchyma  occurs  sometimes  in  roots ; 
c.  <?.,  Raphidophora. 

336.  The  central  cylinder  has,  at  first,  a  peripheral  layer  of 

1  Leitgeb  :  Die  Luftwurzeln  der  Orchideen,  Wien  Akud.  Denkschr.,  xxiv., 
1865,  p.  179. 

FIG  90.  Transverse  section  of  the  central  cylinder  of  a  root  of  a  vascular  cryptogam 
(Marattta  Isevis):  «•,  Internal  layer  of  the  proper  cortex;  p,  endodermis ;  m,  peripheral 
layer  of  the  cylinder;  I,  liber  fascicles;  r,  woody  fascicles ;  c,  conjunctive  parenchyma 
(pith  and  medullary  rays).  (Van  Tieghem.) 


THE   CENTRAL    CYLINDER 


113 


thin-walled  cells 
in  close  union 
with  the  endoder- 
mis :  at  certain 
points  on  this  lay- 
er the  woodj-  and 
the  liber  fasci- 
cles appear,  tin- 
latter  alternating 
with  the  former 
throughout  the 
circle,  and  the 
spaces  between 
them  being  filled 
with  parenchyma. 
337.  The  num- 
ber of  fibro-vas- 
cular  bundles  in 
the  central  cj'lin- 


der  varies  accord- 
ing to  the  class  of 
plants,  and  in  the 
same  plant  accord- 
ing to  the  age  and 
size  of  the  root. 
There  are  generally 
two  in  Cruciferae, 
often  three  in  Er- 
vum  Lens,  four  in 
Ricinus,five  in  Vicia 
Faba,  six  in  Alnus, 
and  eight  in  Fagus  ; 
but  these  numbers 
are  bj'  no  means 
constant. 

338.  The  woody 
part  of  the  bundle 
may  become  re- 


FIG.  91.  Transverse  section  of  the  central  cylinder  of  a  root  of  a  monocotyledon  (Colc- 
casia  antiqnorum) :  e,  internal  layer  of  the  proper  cortex ;  p,  endodennis;  in,  j>eripheral 
layer  of  the  cylinder;  /,  liber  fascicles;  v,  woody  fascicles;  c,  conjunctive  parenchyma 
(pith  and  medullary  rays).  (Van  Tieghem. ) 

FIG.  92.  Transverse  section  of  tlie  cent  ml  cylinder  of  a  root  of  a  dicotyledon  (Artanthe 
elongata)  :  e,  internal  layer  of  the  proper  cortex;  p,  endodennis;  m,  peripheral  layer 
of  the  cylinder;  /,  liber  fascicles;  r,  woody  fascicle;  c,  conjunctive  parenchyma  (pith 
and  medullary  rays).  (Van  Tieghem.) 


112 


MINUTE  STKUUTUKE  OF  THE  HOOT. 


duced  to  a  single  duct,  as  in  some  Carices,  or  there  may  be  a 
large  duct  surrounded  by  smaller  ones  with  or  without  inter- 
vening cells,  or  many  large  and  small  ducts  variously  conjoined. 
Moreover,  there  are  all  degrees  of  compactness  in  the  union  of 
the  different  bundles  of  woody  tissue  with  each  other. 

339.  The  cribrose  part  of  the  bundle  may  be  reduced  to  a 
single  cribrose  tube  (e.g.,  Anacharis),  or  two  or  three  (e.  g.,  Pon- 
tederia) ;  but  usually  there  are  man}',  which  may  be  variously 
disposed. 

340.  Bast-fibres  ma}-  be  associated  with  the  cribrose-cells  in 
the  primary  structure  of  the  root,  and  they  may  be  scattered  (and 
occasionally  with  some  sclerotic  parenctyma)  in  the  cortex.     In 
Philodendron  these  scattered   groups  of  bast-fibres  frequently 
contain  oleo-resin  canals. 


\ 


SECONDARY  STRUCTURE. 

341 .    The  older  parts  of  roots,  even  the  recently  formed  por- 
tions lying  just  back  of  the  root-hairs,  may  undergo  changes 

either  by  the  alteration 
of  their  existing  tissue 
elements  or  by  the  in- 
troduction of  new  ele- 
ments. Some  roots, 
however,  do  not  suffer 
much  change  from  first 
to  last.  Their  cells  may 
become  more  strongly 
cutinized  or  lignified 
as  the  case  may  be, 
but  no  new  elements 
are  brought  in.  This 
is  true  of  the  roots  of 
man}'  monocotyledons, 
but  in  dicotyledons  the 
secondary  changes  are 
generall}'  very  marked. 
The  changes  may  af- 
fect either  the  cortex  or 

the  central  cylinder ;  in  some  cases  the  former  more  than  the 
latter. 


FIG.  93.  Section  through  the  central  cylinder  of  ablnary  root  of  a  vascular  cryptogam 
(Cyatheamedullaris):  e,  internal  layer  of  the  proper  cortex;  p,  endcHlermis;  m,  1*- 
ripheral  layer  of  the  cylinder;  /,  liber  fascicles;  r,  woody  fascicle;  c,  conjunctive  paren- 
chyma (pith  and  medullary  rays).  (Van  Tieghem  ) 


THE   CENTRAL   CYLINDER.  113 

342.  In  the  cortex,  according  to  Olivier,1  the  secondary  tissues 
are  either  parenchymatous  or  suberous  (corky).     The  secondary 
parenchyma   of  the   integument  proceeds  from  the   peripheral 
layer  of  the  central  cylinder.      The  suberous   tissue   in  gym- 
nosperms  and  in  dicotyledons  with  caducous  primary  cortex  is 
derived  from  the  pericambial  layer;  it  is  composed  of  tabular 
cells  with  very  short  radial  walls,  and  begins  to  form  outside 
of  the  primary  liber.     In  the  case  of  woody  dicotyledons  with 
late-formed  secondary  vessels,  and  in  monocotyledons,  it  is  pro- 
duced in  the  external  zone  of  the  cortical  parenchyma,  and  is 
composed  of  cubical  cells. 

343.  In  a  given  species  the  level  of  the  root  where  cork  ap- 
pears depends  on  the  transverse  diameter  of  the  root,  and  also 
on  the  surroundings ;  in  roots  of  the  same  size  the  cork  gen- 
erally appears  earlier,  and  is  more  abundant  in  aerial  than  in 
earth  roots. 

The  cortical  parenchyma  is  renewed  by  layers  of  cells  just  out- 
side of  the  sheath  of  the  central  C3'linder,  and  its  development  is 
wholly  centrifugal. 

344.  The   central    cylinder    undergoes   its    most   remarkable 
changes  as  the  root  grows  older,  in  the  group  of  dicotyledons. 
There  is  very  little  change,  if  any,  in  monocotyledons,  but  in  a 
few  of  the  latter  some  of  the  secondary  changes  now  to  be  de- 
scribed can  be  observed  (e.  g..  Dracaena). 

345.  In  dicotyledons,  including  gymnosperms,  the  thin-walled 
cells  of  the  central  cylinder  are  in  contact  with  the  inner  face  of 
the  endodermis,  and  are  known  collectively  as  the  pericambium. 
Touching  this  pericambium  like  the  two  ends  of  a  bow,  there 
runs  a  mass  of  delicate  cells  behind  each  liber  bundle.     At  the 
point  where  these  bows  touch  the  inner  face  of  the  liber  bundle 
a  group  of  cells  divides  tangentially,  forming  a  cambium  layer, 
which  soon   gives  rise  within    to  new   woody  elements   (often 
coalescent  with  those  of  the  primary  woody  bundles),  and  on  the 
outside   to   new   liber   elements.      These   new   productions  are 
called  secondary  wood  and  liber. 

346.  In  some  cases  —  for  instance  Pinus  —  the  cells  of  the 
pericambium  outside  of  the  primary  woody  bundles  produce  new 
wood  and  new  liber.     The  wood  is  in  contact  with  the  primary 
wood,   while   the   liber   may  serve   to   connect   the  bundles  of 
primary  liber,  thus  bringing  about  a  union  more  or  less  com- 
plete between   similar  elements.      From   these  secondary  pro- 


Annales  des  Sc.  nat.,  ser  6,  tome  xi.,  1881,  p.. 129. 


114 


MINUTE   STRUCTURE  OF   THE   ROOT. 


ductions  come,  of  course,  the  apparently  unbroken  rings  of  liber 
and  the  solid  masses  of  wood  in  old  roots.     If  this  development 

of  new  wood  and 
liber  in  a  perennial 
dicotyledonous 
plant  proceeds 
uninterrupted!}7, 
there  will  exist  at 
the  end  of  the  first 
year  secondary  ele- 
ments in  large 
amount.  After  a 
period  of  rest,  a 
perennial  root  re- 
sumes growth  at 
the  points  where  it 
was  suspended,  and 
the  formation  of 
new  cork,  cortex, 

liber,  and  wood  goes  on  as  before,  until  it  receives  further 
checks.  Owing  to  conditions  to  be  explained  later,  the  charac- 
ter of  the  woody  elements  is 
not  the  same  at  the  begin- 
ning and  end  of  an  active 
period  ;  hence  there  is  gen- 
erally a  clearly  defined  out- 
line bounding  the  product  of  -\  ^UaiOl  ((  IH&rA  ™V* 
growth  of  successive  years. 

347.  More  or  less  of  the 
parenchyma  of  the  original 
cylinder  may  remain  in  the 
form  of  radial  lines  or  of 
bands  (medullary  rays), 
some  of  the  same  sort  of 
tissue  ma}"  be  subsequently 
produced  from  new  points  of  w> 

activity,  and  hence  long  and  short  radii  will  be  met  with. 

FIG.  94.  Section  through  the  central  cylinder  of  a  binary  root  of  a  dicotyledon  (Beta 
vulgaris):  e,  internal  layer  of  the  proper  cortex;  ft,  endodermis;  m,  peripheral  layer  of 
the  cylinder;  /,  liber  fascicles;  r,  woody  fascicle;  c,  conjunctive  parenchyma  (pith  and 
medullary  rays.)  (Van  Tieghem.) 

FIG.  95.  Section  through  the  central  cylinder  of  a  binary  root  of  a  monocotyledon 
(Allium  Opa):  c,  internal  layer  of  the  proper  cortex;  ^,enilodermis;  m,  i>eripheral  layer 
of  the  cylinder:  /,  liber  fascicles;  r,  woody  fascicle;  c,  conjunctive  parenchyma  (pith 
and  medullary  rays).  (Van  Tieghem.) 


TERTIARY   FORMATIONS    IN    THE   ROOT.  115 

348.  The  distinction  of  texture  marking  the  periods  of  rest 
is  not  clear  in  the  liber,  though  even  here  it  may  sometimes  be 
detected.     The  cork  of  the  root  frequently  exhibits  such  dis- 
tinction, but  never  so  clearly  as  does  the  cork  of  stems. 

349.  It  is  a  familiar  fact,  that  the  fleshy  roots  of  many  plants  — 
beets,  and  the  like — exhibit  in  the  first  year  from  seed  concentric 
rings,  which  resemble  those  found  in  perennials.     This  appear- 
ance is  due,  according  to  de  Bary,1  to  the  fact  that  at  an  early 
stage  of  development  (when  the  root  is  only  about  half  a  milli- 
meter thick)  a  new  cambium  zone  is  formed  in  the  parenchyma 
on  the  outer  part  of  the  central  cylinder,  and  this  divides  tan- 
gentially,  extending  therefore  in  a  radial  direction,   producing 
woody  and  liber  elements,  and  at  the  same  time  divides  lateralh', 
so  that  the  whole  constitutes  a  zone  hardly  broken  by  the  rays. 
Soon  a  second  zone  is  produced  in  like  manner,  and  afterwards 
others.     In  all  these  cases  the  elements  are  usually  not  much 
lignified,  but  the  whole  mass  remains  succulent. 

It  happens  sometimes  that  tertiary  formations  are  produced  in 
the  root,  bearing  somewhat  the  same  relation  to  the  secondary 
as  these  do  to  the  primary.  Even  formations  of  higher  order 
are  sometimes  met  with.  But  the  elements  of  all  of  these  are 
easily  identified,  and  their  mutual  relations  can  generally  be  so 
clearly  understood  that  they  do  not  need  special  description. 
The  following  enumeration  embraces  the  most  important  of  these 
formations :  tertiary  cork  and  cortex  ;  fibro-vascular  bundles  in 
secondary  cortex ;  tertiary  liber  and  wood  in  secondary  wood. 
Such  anomalies  are  more  frequent  in  the  stem. 

350.  Roots  branch  by  the  development  of  certain  cells  at  the 
peripheral  layer  of  the  central  cylinder,  and  just  in  front  of  the 
woody  fascicles.2 

The  root  branches  only  laterally  in  flowering  plants ;  in  the 
Lycopodiaceae  there  appears  to  be  terminal  bifurcation,  and  here 
each  branch  shares  with  its  fellow  the  tissue  elements  of  the  root 
from  which  they  both  come. 

1  Vergleichende  Anatomie,  p.  616. 

8  Three  types  of  branching  are  described  by  Janczewski  :  1.  The  mother- 
cells  of  this  layer  (the  so-called  Rhizogenic  cells)  most  frequently  give  rise 
to  all  the  tissues  of  the  rootlet.  2.  They  produce  only  the  central  cylinder 
and  cortex,  but  not  the  root-cap  and  piliferous  layer,  these  being  furnished  by 
the  endodennis  of  the  root.  3.  They  produce  only  the  central  cylinder,  the 
other  tissues  coming  from  the  endodennis  or  from  the  layers  immediately  out- 
side of  it.  The  subsequent  growth  of  the  rootlet  lx>th  in  length  and  thickness 
is  like  that  of  the  root. 


116 


MINUTE   STRUCTURE    OF   THE    ROOT. 


351.  Parasitic  roots,1  or  those  which  fasten  themselves  for 
nourishment  on  other  plants,  are  so  much  modified  by  the  pecul- 
iar conditions  under  which  they  live,  that  they  require  special 
mention.     Their  structure  can  be  best  understood  by  a  section 
through  the  root  of  Cuscuta. 

Here  there  is  no  central  cylinder,  properly  so  called,  nor  is 
there  anything  answering  to  the  root-cap.    The  cortex  is  regarded 

as  reduced 
to  a  pilifer- 
ous  layer, 
since  some 
of  its  cells 
are  pro- 
longed to 
form  a  fasci- 
cle of  long 
hairs  in  inti- 
mate rontm-t 
with  the  tis- 
sues of  the 
host  upon 
which  it  has 
fastened.  In 
the  centre  of 

this  fascicle  of  hairs  some   of  the   elements   are  tracheid-like 
cells,  which  are  in  contact  with  ducts. 

352.  The  roots  of  many  plants  have  distinctive  colors  :    in 
some  the  color  belongs  to  the  wood  (see  402)  ;  in  others  it  is 
due  to  the  cell-sap  ;  in  others,  for  .instance,  the  common  carrot, 
to    orange-colored   crystalline    bodies.      The   crystalline    forms 
found  in  the  parenchyma  of  the  roots  of  the  carrot  are  minute 
rhombs,  or  sometimes  rectangular  plates  to  which  starch-gran- 
ules are  attached.     They  are  associated  with  small  quantities 
of  protoplasmic  matter.     (See  Chapter  IV.,  for  an  account  of 
somewhat  similar  bodies  occurring  in  flowers  and  fruits.) 

353.  The  roots  of  the  higher  Cryptogams  (such  as  Ferns  and 


1  An  exhaustive  paper  on  this  subject  will  be  found  in  Pringsheim's  Jahrb., 
1867  :  Ueber  den  Ban  und  die  Entwicklung  der  Ernahrungsorgaue  parasitischer 
Phaneroganien,  von  Hermann  Grafen  zu  Solms-Laubach.  Koch's  paper  is  in 
Hanstein's  botan.  Abhandlunjren,  vol.  ii.,  1875. 

FIG.  9«.  Vertical  section  of  an  hanatorinm  of  Cnscuta  perforating  the  host-plant. 
ft,  g,  absorbing  hairs :  the  central  cells  are  thickened  at  the  base,  where  they  are  in  contact 
with  the  ducts.  (Koch.) 


ROOTS    OF   CRYPTOGAMS. 


117 


their  allies)  do  not  differ  essentially  from  those  of  Phaenogums  ; 
in  most  cases,  however,  the  terminal  growth,  except  in  the  order 
LycopodiaceiE,  is  from  a  single  apical  cell  instead  of  a  group  of 
cells.  The  apical  cell  produces  not  only  the  tissue  of  the  body 
of  the  root  as  it  extends  in  length,  but  gives  rise  also  to  the 
superficial  cells  at  the  extremity  which  constitute  the  root-cap. 
Lateral  roots  start  from  the  interior  layer  of  the  cortical  paren- 
chyma, and  not  from  the  pericambium  (see  345). 

354.  The  fibro- vascular  bundles  are  concentric  (see  313),  as 
indeed    they    are    in    the 

stems  of  most  of  these 
plants ;  that  is,  the  bast 
part  surrounds  the  wood 
part,  as  if  with  a  sheath, 
even  where  the  latter  part 
is  rudimentary.  There  is 
a  tendency  in  the  root,  less 
marked  than  in  the  stem, 
to  the  production  of  scle- 
rotic cells  of  a  dark  color. 

The  roots  of  the  higher 
cryptogams  do  not  materi- 
ally increase  in  thickness 
after  they  are  first  formed. 

355.  Proper    roots    are 
not  found  in  Muscineae  (the 
mosses  and  hepatics)  ;  the 
absorbing  organs  here  are 
more     strictly     root-hairs. 
These  arise  as  papilla;  from 
the  outer  cells,  and  speedily 
develop   into    tubular   and 
frequently  complex  bodies. 
They     often     become 
branched  in  a  remarkable 
manner,  twisting  and  coil- 
ing around  one  another  like  the  fibres  in  a  thread.     They,  as 
well  as  the  somewhat  simpler  organs  of  the  same  nature,  found 
in  the^ Thallophytes  (such  as  Algo3,  and  the  like),  are  termed 
Rhizoids. 


FIG.  97.  Seedling  of  Cucurbit*  Pepo,  showing  the  main  root,  side  roots,  and  root- 
hairs.    (Sachs. ) 


118  MINUTE   STRUCTURE   OF   THE   STEM. 

Neither  in  Muscineae  nor  Thallopbytes  are  fibro-vascular  bun- 
dles found,  although  in  the  former  the  arrangement  of  elongated 
cells  sometimes  resembles  that  of  the  constituents  of  a  simple 
fascicle.  The  root-like  bodies  by  which  large  sea-weeds  cling 
to  their  supports  are  hold-fasts,  rather  than  true  roots ;  the 
whole  surface  of  the  plant  being  bathed  in  water,  all  parts  can 
probably  absorb  equally  well. 

THE  STEM. 

356.  That  part  of  the  axis  of  the  embryo  which  is  below 
the  cotyledons  is  known  as  the  radicle.      It  is  more  properly 
termed  caulicle  (that  is,  stemlet),   for  its  mode  of  growth  is 
not  like  that  of  the  root,  but  like  that  of  the  stem  above  the 
cotyledons.      The   name   radicle  should    be  restricted   to   that 
which  is  the  beginning  of  the  root,  namely,  the  free  end  of  the 
caulicle.     The  caulicle  is  termed  also  the  hypocotyledonary  stem, 
or  hypocotyl ;  while  for  the  axis  which  is  developed  above  the 
cotyledons,  that  is,  from  the  plumule,  the  name  epicotvledonarv 
stem  may  be  used.     A  large   hypocotyl,   which   has  begun  to 
germinate,  displays  the  structure  of  the  stem  to  good  advantage  ; 
but  the  initial  cells  and  the  nascent  tissues  of  the  stem  must  be 
sought  at  an  earlier  stage,  for  instance,  in  the  plumule  of  a  well- 
forincd  embryo,  as  that  of  Phaseolus  or  Faba.     A  vertical  section 
through  the  plumule,  made  transparent  by  a  clearing  agent  (see 
24),  shows  that  the  cells  have  much  the  same  arrangement  as  in 
the  root-tip,  except  that  no  protective  cap  is  present. 

357.  The  outer  layer  has  divisions  only  at  right  angles  to  the 
surface ;  it  is  continuous  with  the  epidermis  further  back,  and 
is  easily  recognizable  as  nascent  epidermis  (Dermatogen).     En- 
closed by  this  are  layers  which  form  an  arch,  the  nascent  cortex 
(Periblem).     This  encloses  a  mass  of  tissue  from  which  the  fas- 
cicular  system  is  derived  (Plerom).     These  tissues  are  essen- 
tially the  same  in  character  and  development  as  the  corresponding 
nascent  tissues  of  the  root. 

358.  As  the  tissue  elements  develop  from  these  nascent  tis- 
sues, the  stem  is  produced ;  its  structure  is,  however,  generally 
complicated  by  the  early  formation  of  lateral  appendages,  —  leaves 
in  some  of  their  modifications.     Moreover,  the  tissues  of  the 
stem  are  continuous  with  the  tissues  of  the  leaves,  and  it  is  there- 
fore necessary  to  take  into  account  the  mutual  relations  of  these 
two  organs.     The  problem  becomes  still  further  complicated,  in 
a  large  number  of  cases,  by  the  production  of  branches  of  some 


EPIDERMIS    AND   CORTEX.  119 

kind,  the  tissues  of  which  are  of  course  intimately  united  with 
those  of  the  main  axis  from  which  they  are  given  off.1 

PRIMARY  STRUCTURE. 

359.  In  the  stem,  or  ascending  axis,  the  distribution  of  tissue 
elements  is  similar  to  that  in  the  descending  axis,  —  the  root. 
There  is  a  more  or  less  transient  epidermis,  a  cortical  substra- 
tum, and  a  central  cylinder  of  some  kind. 

360.  The   epidermis  of  stems   presents   few   peculiarities   of 
structure  bej-ond  those  already  described  in  Chapter  II.      In 
most  herbaceous  plants  it  persists  with  little  change,  except  in 
the  matter  of  trichomes,  throughout  the  life  of  the  plant ;  but 
in  most  ligneous  plants  it  is  replaced,  often  early,  by  other  pro- 
tective tissues.     Persistent  epidermis  is  found  in  many  woody 
and  half-woody  plants ;   for  instance.  Russelia  juncea,  Leyces- 
teria  formosa,  and  Ptelea  trifoliata. 

In  Palms2  "  the  epidermis  exists  in  old  age  only  in  the  cane- 
like  and  calamoid  stems ;  in  the  rest  it  is  more  or  less  destroyed 
by  the  action  of  the  weather.  In  Calamus  it  consists  of  a  simple 
layer  of  minute  cells  elongated  in  the  direction  from  without 
inward,  and  forms  a  stony,  brittle,  shining  layer." 

361.  The  primary  cortex*  consists  essentially  of  parenchyma 
in  which  isolated  cells  of  a  peculiar  character  may  often  be  found, 
such,  for  instance,  as  crystal  cells,  laticiferous  cells,  tannin  cells, 
and  the  like  (see  292)  ;  and  its  intercellular  spaces  sometimes 
serve  as  receptacles  for  the  various  exudations.      The   paren- 
chyma cells  generally  contain  more  or  less  chlorophyll,  and  some 
starch. 

362.  Immediately  beneath  the  epidermis,  and  not  easily  dis- 
tinguished from  multiple  epidermis,  is  a  portion  of  the  cortex 
known  as  Hypoderma.4     It  is  rarely  sclerotic  parenchyma,  more 

1  In  the  plumule  and  other  buds  all  these  parts  exist  potentially  ;  and  the 
sequence  of  their  development  can  be  successfully  followed  out  by  the  employ- 
ment of  seeds  in  different  stages  of  germination,  or  buds  collected  on  succes- 
sive days  in  spring  and  preserved  at  once  in  alcohol.     In  all  cases  care  must 
be  taken  to  have  the  date  of  collection  of  each  specimen  recorded  in  such  a 
manner  that  no  confusion  can  afterwards  arise. 

2  Mohl  :   Ray  Society,  Reports  and  Papers  in   Botany.     The  Palm-stem, 
Henfrey's  Translation,  1849,  p.  14. 

3  Vesque  (in  Ann.  des  Sc.  nat.,  ser.  6,  tome  ii.,  1875,  p.  82)  gives  a  very  full 
treatment  of  the  subject. 

4  The  word  Hvpoderma  was  introduced  by  Kraus  ( Pringsheim's  Jahrb., 
1865-66,  p.  321),  to  designate  the  layer  of  colorless  cells  under  the  epidermis 
of  leaves,   "das  Analogon  des  Rindencollenchyms."      It  has  since  been  ex- 
tended to  apply  to  the  external  cortex  just  under  the  epidermis  of  stems. 


120        MINUTE  STRUCTURE  OF  THE  STEM. 

frequently  it  is  collenchyma.  Excellent  illustrations  of  the 
latter  kind  of  hypoderma  are  furnished  by  most  Malvaceae  and 
Labiate. 

363.  Schleiden a  distinguished  four  types  of  external  cortical 
.layers  in  dicotyledonous  stems  :    1.  That  existing  as  a  perfectly 
/closed  layer  (penetrated  in  some  cases  only  by  small  canals 

opening  into  stomata) ;  as  in  most  of  the  Cactacae,  Rosa,  Begonia, 
etc.  2.  That  divided  into  many  bundles,  so  that  the  green  cor- 
tical parenchyma  reaches  the  epidermis  ;  e.  g.^  in  Malvaceae,  Sola- 
uaceie,  etc.  3.  That  which  may  be  quite  distinct!}*  recognized 
as  a  special  layer,  but  still  grading  into  parenchyma  at  the 
borders ;  e.  g.,  in  Pyrus  Mains,  Hedera,  Ficus,  etc.  4.  That 
more  completely  merging  into  cortical  parenchyma,  and  therefore 
less  distinct ;  e.  g.,  in  Populus,  Salix,  Sambucus,  etc.  There  are 
some  plants  in  which  it  is  not  distinguishable  ;  e.  ^.,  in  Cheiran- 
thus,  Mesembryanthemum,  etc. 

In  Papaver  and  species  of  Thalictrum  the  cells  of  the  cortex 
next  to  the  epidermis  have  thin  walls,  while  the  zone  next  to  the 
central  cylinder  may  be  sclerotic. 

The  inner  boundary  of  the  cortex  of  the  stem  is,  as  in  the 
root,  the  endodermis.  The  thin-walled  cells  just  within  it  form 
the  peripheral  layer  of  the  central  cylinder,  or  shaft. 

364.  Variations  in  the  cortex  consist  chiefly  in  one  of  the 
following   modifications:    1.    Increase  of  its  layers,  sometimes 
to  an  extraordinary  extent,  and  often  accompanied,  especially 
in  water-plants,  by  the  formation  of  large  air-bearing  intercellular 
spaces.     The  student  should  examine  the  peculiar  structure  of 
the  cortex  at  the  nodes,  in  these  cases  of  spongy  cortex.     2.   It 
has  been  previously  shown  (215)  that  collenchyma  is  a  common 
modification  of  cortical  parenchyma.     A  variation  in  structure 
reaching  the  same  end  as  collenchyma,  namely,  strengthening 
the  stem,  is  found  in  a  great  number  of  plants ;  the  cortical 
parenchyma,  especially  at  the  outer  part,  becoming  conspicuous!}' 
sclerotic,  and  the  tissue  very  compact.     3.  Fibres  ma}'  occur  in 
the  cortex,  either  isolated  or  in  small  fascicles. 

365.  The  primary  flbro-vascnlar  bundles  of  the  stem  are  de- 
veloped at  definite  points  in  the  peripheral  layer  of  the  central 
cylinder.      Their  structural  elements,  wood  and  liber,  vary  as 
regards  their  relative  amount,  even  in  the  same  plant.      A  given 
bundle  may  and  generally  does  change  much  during  its  course, 
interlacing  here  and  there  with  other  bundles,  and  giving  off 
branches  at  different  points. 

1  Principles  of  Scientific  Botany,  p.  240. 


COLLATERAL   BUNDLES. 


121 


When  corresponding  bundles  of  plants  of  different  groups  are 
compared  together,  some  diversities  as  regards  the  arrangement 
of  the  wood  and  liber  elements  are  exhibited ;  but  most  of  the 
cases  can  be  referred  without  difficult}*  to  the  class  of 

366.  Collateral  bundles  (see  313)  of  the  ordinary  type  ; 
namely,  those  having  liber  on  the  external  aspect  and  wood  on 
the  internal  aspect.  In  some  cases,  however,  this  order  may  be 
exactly  reversed  ;  e.g.,  in  the  cortical  fascicles  of  Calycauthaceae. 
The  wood-elements  in  collateral  bundles  are  generally  arranged 
in  radial  series  ;  the  inner  ducts  or  their  equivalents  (tracheids) 
being  more  slender  and  having  more  closely  coiled  spiral  mark- 
ings than  those  nearer  the  periphery  of  the  bundle.  The  radial 
series  may  be  in  close  contact,  separated  by  very  thin  plates 
of  parenchyma,  or 
may  have  a  large 
amount  of  this  tis- 
sue between  them. 
In  dicotyledons,  as 
a  rule,  the  ducts 
at  anv  <iiven  dis- 
tance from  the  cen- 
tre of  the  stem  have 
a  noticeable  uni- 
formity, so  that  a 
cross-section  of 
the  primary  tissue 
shows  a  number  of 
concentric  circles  of 
ducts  of  the  same 
size.  Sometimes, 
however,  the  ducts 
in  a  radial  series 
may  l>e  reduced  to 
one.  In  stems  of  monocotyledons  there  is  less  regularity  in  the 
arrangement  of  the  wood-elements,  but  there  is  a  substantial 
likeness  in  their  structure  in  any  group.  They  are  generally  in 
the  form  of  a  blunt  wedge,  the  apex  towards  the  centre  of  the 
stem,  the  space  between  the  inclined  sides  of  the  wedge  being 
mostly  occupied  by  small  ducts,  wood-cells,  and  fibres. 

FIG.  98.  Transverse  section  of  a  collateral  fibre-vascular  bundle  of  the  stem  of  Indian 
corn :  p,  p.  conjunctive  parenchyma;  a,  onter  face;  i,  inner  face  of  the  closed  fibre-vas- 
cular bundle,  which  consists  of  a  xylem  portion  (g.g,  two  large  pitted  ducts;  »,  spirally 
n.-kened  duct;   r,  isolated  ring  of  an  annular 'duct;  /,  aeriferons  lacuna,  caused  by 
imng  resulting  from  growth)  and  a  plilogm  portion,  r,  r.    The  whole  bundle  is  sur- 
rounded by  a  bundle-sheath  of  thick-walled  cells.    (Sachs ) 


122  MINUTE   STRUCTURE   OF   THE   STEM. 

367.  The  cribrose  portion  of  a  collateral  bundle  often  has,  in 
addition  to  true  cribrose-cells,  prismatic,  thin-walled  cells,  known 
as  cambiform  cetts.1 

368.  According  to  Vochting 2  the  cambiform  and  cribrose  cells 
appear  in  some  cases  to  have  a  common  mother-cell,  which  di- 
vides obliquely  in  the  direction  of  its  length.     The  cambiform 


cells  may  divide  by  transverse  partitions,  and  if  the  cells  are 
moderately  large  the  last  divisions  may  be  parenchymatous.  In 
most  monocotyledons  and  dicotyledons  the  cribrose-cells  are  much 
larger  than  the  cambiform  ones,  and  their  cross-sections  are  distin- 
guished by  being  less  sharply  quadrangular.  In  many  succulents 
there  are  also  very  small  cells  resembling  undeveloped  cribrose- 
cells. 

369.  The  cribrose  and  woody  parts  of  a  collateral  bundle  are 
generally  distinguishable  from  each  other  by  the  lignified  char- 

1  De  Bary  reserves  for  these  cells  the  term  Cambiform,  which  was  used  by 
Nageli  in  a  wider  sense. 

2  Beitrage  zur  Morphologic  und  Anatomie  der  Rhipsalideen,  Pringsheim's 
Jahrb.,  1874,  p.  327. 

FIG.  99.  Transverse  section  of  a  part  of  the  central  cylinder  of  the  mature  hypocoty- 
ledonary  portion  of  the  stem  of  Ricinus  communis:  r,  parenchyma  of  the  primary 
cortex;  m,  of  the  pith;  between  rand  b  is  the  simple  endodermis  containing  starch- 
grains;  the  fibro-vascular  bundle  is  made  up  of  the  phloem  b,  y.  the  xylem  ft,  t,  and  the 
cambium  c,  c ;  cb,  interfascicular  cambium.  In  the  phloem  are  the  bast-tibres  6,  b,  the 
soft  bast  y,  y  (partly  parenchyma  and  partly  cribrose-tubes);  in  the  xylem,  small  pitted 
ducts  t,  t,  wider  pitted  ducts  g,  g,  and  between  them  wood-fibres.  (Sachs.) 


BUNDLES   OF   THE   STEM. 


123 


acter  of  the  latter  and  the  softer  texture  of  the  former.  As  has 
been  before  noticed  (see  345),  in  dicotyledons  and  gymnosperms 
in  which  there  is  annual  increase  in  diameter  there  is  a  layer 
of  peculiar  merismatic  tissue  (cambium)  between  the  two  parts. 
It  is  generally  easy  to  identify  the  cells  of  this  cambium  layer,  on 
account  of  their  elongated  form  and  intimate  contact  with  each 


other.  Their  development  gives  rise  (1)  to  new  cells  like  them- 
selves, (2)  to  cribrose  and  (3)  to  woody  elements ;  all  of  which 
are  to  be  examined  later,  under  "  Secondary  Structure." 

370.  The  sheaths  of  collateral  bundles  may  have  the  character 
of  typical  endodermis  and  envelop  the  single  bundles,  or  may 
consist  of  strands  of  long  fibres  (hard  bast),  which  are  on  one 
side  of  the  cinbrose  portion,  and  accompany  the  bundle  through 
its  whole  course  in  the  stem.     The  strands  of  fibres  frequently 
encroach  upon  the  cribrose  part  of  the  bundle  so  much  as  to  be 
more  or  less  commingled  with  it  (see  311). 

371.  The  stem  may  sometimes  have  bicollateral  bundles  either 
(1)  with  the  woody  part  on  the  interior  as  well  as  on  the  exterior 
aspect  (e.  g.,  Cucurbitaceae),  or  (2)  with  an  envelope  of  wood 
surrounding  the  liber ;  this  envelope  is  seen  at  the  extremities  of 
the  bundle,  while  the  rest  of  it  has  the  ordinary  character  (Iris). 

372.  The  bundles  of  the  stem  may  be  concentric  (see  313)  ;  a 

FIG.  100.  Longitudinal  section  of  a  fibro-vascular  bundle  of  Ricinus  (the  cross-section 
being  shown  in  Fig.  99):  r,  cortical  parenchyma;  gs,  bundle-sheath;  6,  bast-fibres; 
p,  phloem-parenchyma;  c,  cambium  (the  row  of  cells  between  c  and  p  develops  after- 
wards into  a  cribrose-tube) ;  in  the  xylem  portion  of  the  bundle  the  elements  are  devel- 
oped successively  from  «  to  t' ;  »,  the  first  slender  and  long  spiral  duct;  s',  wide  spiral 
duct,  the  spiral  band  uncoiling ;  I,  duct,  thickened  partly  in  a  scalariform,  partly  in 
a  reticulate  manner;  h,  h',  h",  h'",  wood-cells;  t,  pitted  duct;  </,  absorbed  septum; 
t',  pitted  duct,  still  young;  in  /,  t,  And  t'  the  boundary  lines  of  the  adjoining  cells  which 
have  been  removed  are  shown  in  the  wall  of  the  ducts;  m,  parenchyma  of  the  pith. 
(Sachs.) 


124  MINUTE   STKUCTUKE   OF   THE    STEM. 

ring  of  liber  ma}-  surround  the  whole  of  the  woody  portion,  or 
the  wood  may  surround  the  liber.  The  former  of  these  arrange- 
ments is  common  in  the  vascular  cryptogams  (see  354). 

373.  The  pith  of  the  stem  consists  of  parenchyma  frequently 
intermingled  with  other  structural  elements  in  small  amount,1 
especially  long  fibres,  woody  prosenchyma,  and  latex-cells. 

The  parenchyma  cells  of  pith  have  been  classified  in  the 
following  manner:  (1)  active  cells,  having  the  office  of  storing 

starch  and  other  assimilated 
products  for  a  time ;  (2)  crys- 
tal-cells, in  which  ciystals  are 
formed  ;  (3)  inactive  cells, 
which,  having  lost  the  power 
of  receiving  starch  or  other 
products,  remain  empty. 

These  apparently  unimpor- 
tant distinctions  have  been 
shown  bj*  Gris 2  to  be  valuable 
in  the  identification  of  consid- 
erable groups  of  plants.  Pith 
composed  of  active  or  inactive 
cells  alone  is  termed  by  him 
homogeneous  ;  that  which  con- 
tains more  or  less  of  both  kinds  of  cells,  heterogeneous.  The 
arrangement  of  the  elements  in  heterogeneous  pith  is  so  nearly 
constant  as  to  have  much  interest  for  the  systematist. 

374.  The  medullary  rays  comprise  the  conjunctive  parenchy- 
ma, which   lies   between   the   bundles  in  the  stems  of  normal 
dicotyledons.     The  cells  are  for  the  most  part  much  flattened 
radially,  always  so  in  those  cases  where  the  bundles  are  closety 
approximated  (see  also  207). 

375.  The  stem  develops  from   the  bud  by  extension  of  its 
internodes.    When  these  have  attained  a  certain  length,  different 

1  The  peculiar  structures  found  occasionally  in  the  periphery  of  the  pith  of 
Sambucus,  and  sometimes  in  the  bark,  have  been  mistaken  for  fungi,  but  have 
been  shown  by  Oudemans  and  by  Dippel  to  be  receptacles  for  a  very  heteroge- 
neous mixture  of  tannin  and  other  matters  ( Verh.  d.  Nat.  Vereins  d.  Preussens, 
Rheinlande  und  Westphalens,  1866,  p.  1). 

2  A  detailed  account  of  the  orders  of  plants  examined  by  Gris  will  be  found 
in  Nouvelles  archives  du  Museum,  t.  vi.  fasc.  3,  4,  p.  201  (9  plates).     An  extract 
from  the  same  is  given  in  Ann.  des  So.  nat.,  se>  5,  tome  xiv.,  1872,  p.  34. 

PIG.  101.  Clethra  alnifolia  longitudinal  section  through  the  retlculat«d  pith  of  a 
young  brand. ;  each  active  <-ell  .-onmim.  a,  nucleus  and  chlorophyll  grains,  December. 
(Gris.) 


COURSE    OF    THE    BUNDLES    IN   THE    STEM.  125 

for  different  stems,  and  depending  often  on  some  external  con- 
ditions, the}'  do  not  further  elongate ;  but  those  tissues  of  the 
internodes  by  which  growth  in  length  has  taken  place  become 
gradually  firmer,  and  constitute  permanent  tissue.  It  sometimes 
happens  that  the  nodes  and  internodes  of  the  stem  are  not  plainly 
distinguishable  from  each  other.  This  is  the  case  in  most  palms, 
where  the  growth  takes  place  from  the  terminal  bud  alone. 

376.  Even  a  cursory  examination  of  the  structure  of  a  stem 
which  has  thus  unfolded  from  a  bud  shows  that  the  number  and 
the  distribution  of  the  bundles  have  much  to  do  with  the  number 
and  the  arrangement  of  the  leaves.    Comparative  investigations  * 
of  large  orders  of  vascular  plants  have  shown  that  the  number 
of  the  bundles  of  the  stem  always  bears  some  relation  to  that  of 
the  leaves  at  a  given  portion  of  the  axis,  and  to  the  arrange- 
ment of  the  leaves.     "The  more  bundles  in  a  given  leaf,  and 
the  greater  the  number  of  leaves  in  a  cycle  or  whorl,  the  more 
numerous  will  be  the  bundles  in  the   stem  at  that  level.      In 
monocotyledons  with  a  large  crown  of  leaves  these  two  condi- 
tions are  met  with,  and  in  these  stems  arc  found  the  greatest 
number  of  bundles."  2 

377.  Course  and  distribution  of  the  bundles  in  the  stem.     In 
the  internodes,  the  bundles  mostly  run  parallel  to  the  axis,  or  in 
curves  of  very  long  radius ;   at  the  nodes,  they  may  interlace 
transversely.     If  a  bundle  is  followed  through  its  course  from 
below  upwards,  it  will  be  found  to  branch  at  some  of  the  nodes ; 
the  branch  of  the  bundle  going  directly  into  the  leaf  at  that 
point,  or   else  passing   upwards   through  other  nodes   until   it 
reaches  a  leaf,  the  number  of  nodes  traversed  varying  according 
to  the  kind  of  plant  and  the  region  of  the  stem.8     More  than 
one  branch  of  the  bundle  ma}',  however,  go  to  a  single  leaf. 

378.  If,  now,  the  course  of  the  bundle  be  examined  from 
above  downwards,  it  can  be  seen  that  each  leaf  contributes  its 
simple  or  compound  fascicle  to  the  larger  bundle  with  which  that 
from  the  leaf  sooner  or  later  becomes  confluent.     The  fascicle 
from  the  leaf  can  frequently  be  followed  down  for  several  inter- 
nodes as  a  separate  thread,  the  so-called  foliar  trace.     If  such 
foliar  traces  are  nearly  isolated  in  their  course,  a  cross-section 
of  the  stem  will  give  a  ground-plan  of  the  leaf-arrangement. 
Usually,  however,  there  is  much  complexity  in  the  distribution 

1  Nageli  :  Beitrage  zur  wissensch.  Botanik,  1858,  and  Hanstein :  Prings- 
heim's  Jahrb.,  1858. 

2  Van  Tieghem :  Traite  de  Botanique,  1884,  p.  746. 
8  Van  Tieghem  :  Traite  de  Botanique,  1884,  p.  733. 


126 


MINUTE   STRUCTURE   OF  THE   STEM. 


of  the    fascicles,    and    they 
curve    considerably   in    their 
course,  so  that  it  is  often  dif- 
ficult to  follow  the  foliar  trace 
for   more   than   a   short  dis- 
tance.    If  the  stem  has  alter- 
nate leaves,  the  direction  of 
the  foliar  traces  will  of  course 
be   different  from    that  in  a 
stem  with  opposite  or  verti- 
cillate    arrangement    of    the 
leaves.    The  following  figures 
exhibit  the   course  and  dis- 
tribution in  a  few  cases  :  — 
In  the  leafy  shoot  of  Clem- 
atis, Fig.  102,  the  leaves  are 
opposite  and  decussate.  From 
each  leaf  there  descend  three 
fibro-vascular    bundles  ;    for 
instance,  at  the  lower  node 
there  are  a,  b,  c,  and  e,  f,  d. 
The  leaves  at  the  node  next 
above   decussate  with    those 
below  ;    each    of    them    has 
three  fibro-vascular  bundles, 
respectively,  »',  g,  I, 
and  Jc,  A,  w,  which 
become       somewhat 
smaller  as   the}'  de- 
scend  to    the    next 
node,  where  they  be- 
come   blended    with 
the    bundles    there. 
An  examination   of 
the  third  node  shows 
that  the  two  leaves 
there  contribute  bun- 
dles to  the  axial  cyl- 
inder; there  is  again 
a  blending  of  the  bundles  at  the  node  below. 

FIG.  102.  Diagrammatic  view  of  a  leafy  stem  of  Clematis,  showing  the  arrangement  of 
the  flbro- vascular  bundles:  a,  b,  c,  —  e.f,  rf,  the  fascicles  from  the  lower  j>air  of  leaves; 
i,  g,  l,  —  k,  h,  m,  the  fascicles  from  the  second  pair  of  leaves;  q,  r,  s,—p,  n,  o,  the 


DISTRIBUTION   OF   THE   BUNDLES   IN   THE   STEM.      127 


Both  lateral  strands  of  a  leaf  in  such  a  case  as  this  run  down 
through  one  internode,  bend  outwards  at  the  node  below,  and 
attach  themselves  to  the  lateral  strands  belonging  there. 

Suppose,  now,  that  a  cross-section  of  the  stem  of  Clematis  is 
made  at  the  lowest  node  represented  in  Fig.  102  ;  all  the  fibro- 
vascular  bundles  at  that  point  will  be  seen  in  their  relative  posi- 
tions, some  of  them  cut  squarely  off, 
others   oblique!}',   according   to  curves 
which   they  make.     A  cross-section  in 
the  internode  above  would  show  slen- 
derer bundles,  but  all  arranged  in  much 
the  same  manner  as  in  the  thicker  inter- 
node below  ;  that  is,  in  a  circle.1 

The  circle  is  made  up  of  fibro-vas- 
cular  bundles  which  have  an  inner  por- 
tion of  wood  ;  within  the  circle  is  paren- 
chyma (the  pith),  and  outside  of  it  more 
parenchyma  (the  cortex),  which  can  be 
stripped  off  with  the  bast-portion  of  the 
central  cylinder  as  bark. 

Compare  Fig.  102  with  Fig.  103.  In 
the  latter,  the  stem  does  not  exhibit  in 
cross-section  the  fibro-vascular  bundles 
arranged  in  a  circle :  they  are  more  or 
less  scattered  ;  there  is  no  clearly  de- 
fined central  portion  nor  well-marked 
outer  portion  free  from  them.  Hence  it 
cannot  be  said  that  such  a  stem  has  any 
distinction  of  pith,  wood,  and  bark. 

A  further  distinction  may  be  here 
noted  ;  namely,  that  the  bundles  in  Fig. 
102  have  the  power  of  increasing  in 
thickness,  adding  new  wood  and  new  bast  to  the  primary  struc- 

1  Another  feature  must  be  attentively  studied  ;  namely,  the  relation  of  the 
forming  bundles  to  the  young  leaves  at  the  upper  part  of  the  stem.  One  may 
say  the  bundles  descend  from  the  leaf  to  the  stem,  or  ascend  from  the  stem  to 
the  leaf.  But  since  the  development  of  the  leaf  part  and  the  stem  part  of  a 
bundle  goes  on  together,  these  terms,  ascend  and  descend,  should  be  under- 
stood to  refer  to  our  method  of  tracing  the  bundles  out,  and  not  to  the  method 
of  their  development. 

fascicles  from  the  third  pair  of  leaves;  x,  t,  fascicles  of  the  fourth  pair  of  leaves;  ft,  a,  — 
y,  S,  pairs  of  undeveloped  leaves  not  as  yet  having  fascicles.  The  diagram  illustrates 
both  Clematis  Viticella  and  C.  Vitalba.  (Nageli. ) 

FIG.  103.  Longitudinal  section  through  the  stem  of  Aspidistra  elatior,  showing  the 
curved  course  of  the  flbro-vascular  bundles  in  the  simplest  palm-type.  (Falkenberg.) 


128 


MINUTE  STRUCTURE  OF  THE  STEM. 


ture  (see  390)  ;  but  in  Fig.  103  the  bundles  are  closed  (see  315), 
and    incapable  of 

*        Jf           4       ?~^       ^              further  increase  in 

.  c  (    r  } 

\5     *    thickness.    Hence 

^  K 

A 

^          any  further  growth 

I 

\          in  thickness  of  the 

* 

ITVII          »v-~ 

4    -m    v 

-  ^\        stem     shown      in 

11    A 

n   11 

^  A           Fig.  103  must  be 

by   the   intercala- 

V 

tion  of  new  bun- 

"  1  1  " 

N        11         A 

A        dies. 
379.  It  was  held 

by   Dcsfontaines  J 

1 

that  the  new  vas- 

1 1  I 

cular    bundles   in 

11  M 

Talras  originate  in 

wfi  k\k\ 

i  Quoted  l.y  M..hl, 

i   n 

in   The   Stmcture   of 

the   Palni-Stfiii   (The 

Ray  Society,   Reports 

and    Papers  on   Bot- 

1 

any;  London,  1849). 

Another  illustration 

of  the  arrangement  of 

fibro-  vascular  bundles 

is  here  given  :  — 

The  stem  of  the  Vi- 

f    1       * 

U;    11 

a    tis  vinifera  is  usually 

1    "\  '  k 

V     i\      11  cv 

'y              regarded    as     sympo- 

V 

\           1      1  / 

l           ilial  ;  that  is,  it  is  com- 

1 

posed    of    iutci  -nodes 

belonging  to  different 

1 

axes  (see  vol.  i.  pp.  54 

1 

and    154).      In    this 

species    of    grapevine 

1 

two  leaves  in   succes- 

1 

sion  have  a  tendril  on 

the  opposite  side,  then 

follows  a  leaf  without 

1 

anv  tendril,  next  the 

104                                              sequence  of  two  with 

FIG.  104.  Diagrammatic  projection,  showing  the  disposition  of  the  flbro-vascular  bun- 
dles in  a  leafy  shoot  of  Vitis  vinifera.  Each  leaf  has  five  fascicles,  which  are  unsymme- 
trically  arrangeil :  n.  l>,  c,  d,  e :  h,  i,  /.-.  /,  m ;  o.  ;>,  q,  r,  x  ;  u,  r,  w,  x,  y :  a,  ft,  y,  «,  e  ;  >|.  <, 
0,  i,  K.  Each  tendril  lias  three  fibro-vascular  bundles  passing  in  from  the  stem,  g,  I,  '-  ; 
the  axillary  buds  have  also  three,/and  n.  (Nageli.) 


STEMS   OF   MONOCOTYLEDONS    AND    DICOTYLEDONS.      129 


the  centre  of  the  stem,  and  that  the  hard  and  thick  vascular 
bundles,  situated  at  the  periphery  of  the  stem,  are  older  than 
the  softer  ones  occupying  the  centre.  For  stems  like  those  of 
Palms  he  used  the  term  endogenous,  giving  the  name  exogenous 
to  the  other  class,  in  which  new  layers  are  added  to  the  outside 
of  the  wood.  The  terms  endogenous  and  exogenous  were 
adopted  by  De  Candolle,  and  have  pla3'ed  an  important  part 
in  Systematic  Botany.  Comparative  researches  have  shown  that 
the  term  endogenous  as  applied  to  the  growth  of  stems  like 
those  of  Palms  is  not  appropriate,  and  hence  the  correlative 
words  have  been  generally 
abandoned  as  names  of  the 
two  great  groups  of  plants. 
They  are  now  generally  re- 
placed by  the  words  monocoty- 
ledonous  and  dicotyledonous 
(see  Vol.  I.  p.  69). 

Moreover,  it  is  now  gener- 
ally admitted  that,  although 
the  distinctions  pointed  out  in 
366  —  namely,  those  relating 
to  the  arrangement  and  course 
of  the  bundles  —  are  valid  for 
most  plants  of  the  two  great 
groups,  monocotyledons  and 
dicot3'ledons,  thej'do  not  hold 
for  all. 

380.  Instead  of  describing 
the  numerous  exceptions  to 
both  of  these  groups  as  ex- 
ceptions, many  authors  have 
endeavored  to  construct  some 
new  classification  which  shall 
embrace  most  of  the  anoma- 
lies in  one  or  more  co-ordinate  divisions.  Of  these  attempted 

tendrils  is  resumed.  Every  leaf  has  five  fibro- vascular  bundles,  which  are 
arranged  unsvirmietrically,  as  shown  in  the  fisiure.  The  long  distance  through 
which  some  bundles  can  run  before  uniting  with  any  others,  and  the  differences 
in  structure  at  the  successive  nodes,  are  clearly  exhibited  in  the  diagram. 

FIG.  105.  Diagrammatic  projection  of  the  disposition  of  the  fibro-vascniar  buwlles  in 
Phaseolus  vulgaris.  This  diagram,  like  Fig.  104,  supposes  two  longitudinal  sections, 
both  seen  from  the  :i  xio  :  a,  b,c,tl ;  f.  ft,  h,  i:  >,m,n,o;  q,r,x,t;  w,  r ,  w,  x ;  the  succes- 
sive leaf-traces,  each  with  four  fascicles.  Of  the  upper  leaf-trace,  the  first  two  fascicles, 
y,  z,  are  visible,  e,  k,  k,  p,  fascicles  for  the  three  leaves  below.  Nageli.) 
9 


130 


MINUTE   STRUCTURE  OF  THE   STEM. 


classifications  only  one  will  be  given  here,  and  that  only  in  part 
and  somewhat  rearranged  ;  namely,  de  Bary's  :  — 

I.  The  palm- type.  A  cross-sec- 
tion of  most  monocotyledons  shows 
that  the  bundles  are  not  arranged 
in  a  simple  ring,  but  that  they  are 
irregularly  scattered  or  more  or 
less  crowded  to  form  a  shaft,  which 


may  be  hollow  as  in  most  grasses,  or  filled  in  the  centre  with 
parenchyma  through  which  scattered  bundles  run.  The  periphery 
of  this  cylinder  or  shaft  is  not  a  true  bark,  nor  is  the  middle  a 
true  pith.  In  the  simple  palm-type,  all  the  bundles  are  leaf- 
strands. 

II.  The  dicotyledonous  type,  in  which  all  the  primary  bundles 
are  leaf- trace  threads.  The  bundles  are  arranged  in  a  simple 
circle  within  which  is  pith,  outside  of  which  is  cortex ;  medullary 


FIG.  106.  Transverse  section  through  the  outer  part  of  the  stem  of  Kunthia  mon- 
tana,  a  Palm.  (Mohl.) 

FIG.  107.  Transverse  section  through  the  middle  part  of  the  stem  of  Corypha 
CCrifera,  a  Palm.  (Mohl.) 


STRUCTURE   OF   PALM-STEMS.  131 

rays  run  between  the  parenchyma  of  the  pith  and  that  of  the 
cortex.  To  this  type  belong  most  dicotyledons,  Couiferae,  and 
Gnetaceae  (with  the  exception  of  Welwitschia1). 

III.  Anomalous  dicotyledons,  differing  from  the  last  in  not 
having  all  their  primary  bundles  arranged  in  a  simple  circle. 
The  extra  bundles  may  either  be  in  the  cortex,  as  in  some  Mela- 
stomaceae  and  Rhipsalideae,  or  they  may  lie  in  the  pith  either 
scattered  or  arranged  in  rings,  as  in  Cucurbitaceae,  the  herba- 
ceous Berberidaceae,  species  of  Papaver,  Thalictrum,  Amaran- 
tus,  and  Phytolacca,  many  Nymphaeaceae,  some  Begoniaceae,  and 
a  few  species  of  Aralia. 

De  Bary's  other  classes  comprise  anomalous  monocotyledons 
and  certain  higher  ciyptogams. 

381.  To  make  clearer  the  somewhat  complicated  structure  of 
palm-stems  which  have  unfortunately  been  selected  in  many  text- 
books to  illustrate  the  histology  of  monocotyledons,  a  few  general 
statements  are  now  given  as  introductory  to  the  special  treatment 
in  the  note.2  That  portion  of  a  palm-stem  which  lies  above  the 
lowest  active  leaves  (better  called  fronds)  is  of  a  conical  shape, 
is  often  much  elongated,  and  carries  all  the  new  and  forming 

1  For  a  description  of  this  interesting  plant,  and  an  account  of  its  peculiari- 
ties of  structure,  consult  J.  D.  Hooker  on  Welwitschia. 

2  The  exposition  by  de  Bary  of  the  structure  of  the  simpler  forms  of  Palms  is 
given  nearly  in  full  in  the  translation  which  follows  :  — 

"  Since  the  appearance  of  Mohl's  Palmenanatomie,  the  following  main  char- 
acters have  been  recognized  as  belonging  to  the  simple  palm-type. 

"  All  the  bundles  in  the  cylinder  (with  some  doubtful  and  certainly  extremely 
insignificant  exceptions  which  will  be  mentioned  later)  are  leaf-traces.  The 
base  of  the  leaf  includes  the  whole  circumference  of  the  stem,  or  at  any  rate 
the  greater  part  of  it.  The  leaf-trace  is  always  several  threaded  :  generally  it 
consists  of  many  threads,  in  stout  stems  even  of  a  couple  of  hundred ;  its  width 
is  nearly  the  whole  of  the  circumference  of  the  stalk.  From  the  base  of  the  leaf 
the  threads  curve  down  into  the  cylinder,  within  which  they  descend,  some  in 
its  outer  surface  and  nearly  radial  and  perpendicular,  others  radial  and  oblique, 
first  pressing  inward  toward  the  long  axis  of  the  cylinder  in  a  curve  which  is 
convex  towards  the  upper  and  inner  side  of  the  stem,  then  curving  outward, 
and  gradually  passing  towards  the  outer  surface  of  the  cylinder,  and  in  propor- 
tion as  they  approach  this,  approximating  towards  a  perpendicular  position. 
All  threads  descend  through  many  internodes,  and  unite  at  last  in  the  outer 
portions  of  the  cylinder  with  others  which  enter  it  further  down,  attaching 
themselves  to  these  in  a  direction  which  is  sometimes  tangential,  sometimes 
radial,  and  sometimes  oblique.  Until  this  attachment  of  their  lower  ends,  the 
bundles  run  independently.  The  union  of  the  lower  ends  of  bundles  with 
others  that  enter  the  cylinder  lower  down  generally  takes  place  in  such  a  way 
that  the  whole  number  of  the  bundles  in  successive  internodes  of  equal  cir- 
cumference remains  about  the  same.  As  the  successive  internodes  and  leaves 


132 


MINUTE   STRUCTURE   OF   THE   STEM. 


leaves.  It  is  known  as  the  Phyllophore.  The  newest  leaves  are 
formed  nearest  the  apex  of  this  cone  ;  and  here,  as  before  shown, 
all  the  fibre-vascular  bundles  common  to  the  leaves  and  stem  origi- 
nate. In  most  cases  there  is  absolutely  no  increase  in  thickness 
of  the  stem  below  the  base  of  this  cone  ;  but  as  the  apex  of  the 
cone  is  developed  and  extends  further  upwards,  thus  elongating 
the  stem,  there  is  also  a  growth  in  thickness  of  the  part  of  the 
cone  just  above  its  base.  Thus  a  uniform  size  of  the  cylindrical 
stem  is  kept.  But  such  increase  in  thickness  cannot  continue 
below  the  point  at  which  there  are  active  leaves. 

increase  in  size,  the  number  of  bundles  grows  larger,  and  conversely.  The 
number  of  internodes  through  which  a  bundle  passes  cannot  be  fixed  with 
exactness. 

"  Those  bundles  in  a  leaf- trace  which  curve  like  a  bow  towards  the  middle  of 
a  cylinder  do  not  penetrate  to  equal  depths  ;  as  a  general  thing,  the  median 
bundle  of  a  series  lies  deepest,  and  the  others  lie  less  deep  in  proportion  to  their 
distance  from  this  ;  the  marginal  ones  descend  nearly  perpendicularly  in  the 
outer  surface  of  the  cylinder.  Where  there  are  several  series  of  bundles,  those 
in  the  inner  series  generally  penetrate  more  deeply  than  those  in  the  outer 
ones  which  lie  at  an  equal  distance  from  the  median  thread. 

"The  necessary  consequences  of  the  course  described  are  :  first,  that  in  the 
cross-section  of  an  internode  the  bundles  stand  closer  together  in  proportion  as 

they  are  nearer  to  the  outer 
surface  of  the  cylinder,  — 
a  phenomenon  which  is 
especially  noticeable  when 
the  bandies  are  distributed 
over  the  whole  surface  of 
the  cross-section  of  the 
cylinder  ;  second,  the  suc- 
cessive traces  dwindle,  and 
their  curving  threads  cross 
each  other.  Mohl's  cele- 
brated plan,  which  is  here 
reproduced  in  Fig.  108,  ex- 
hibits this  latter  relation 
in  a  radial  longitudinal 
section,  being  based  on 
the  untenable  assumption 
that  all  the  threads  of  a 
trace  are  nearly  equally 
curved,  and  are  placed  in 
a  tangentially  perpendicu- 
lar direction,  so  that  they 
form  in  the  outer  surface 
an  open  curving  cone.  1 1  it 

£10"  !™    ™"lll>§  (liaeram  of  the  «"»•««  of  the  nbro-vascniar  bundle*. 
*  m.  109.  Diagram  of  the  course  of  rtbro- vascular  bundle*  in  a  palm-stem  with  dis- 
ucnous  leaves.    (JDe  Bary.) 


STEMS   OF   MONOCOTYLEDONS.  133 

382.  Branner1  has  shown  that  the  bundles  in  Palms  do  not 
end  blindly  at  their  lower  extremities  upon  the  surface  of  the 
stem,  but  that  they  are  connected  in  sections  or  divisions  from 
base  to  summit  one  with  another,  and  one  on  top  of  another. 
He  has  further  shown  that  each  bundle  lies  in  a  spiral  curve 
within  which  it  grows ;  and  whether  it  returns  to  the  surface 
upon  the  side  in  which  it  originated  or  upon  the  opposite  side,  it 
is  always  in  this  curve. 

383.  The  structure  and  development  of  monocotyledons  have 
received    much    attention    during  the  last  few  years,  and  the 
results  obtained  have  caused  some  modification  of  previously 
existing  classifications.      Two  of  the  proposed  methods  of  re- 
arrangement are  herewith  given  :  — 

384.  Falkenberg  recognizes  the  three  following  types  of  stems 
of  monocotyledons. 

I.  The  tissue  of  the  central  cylinder  is  not  plainly  separable 
even  in  its  mature  state  into  conjunctive  parenchyma  and  fibro- 
vascular    bundles.      (To    this    type    belong    the    water-plants, 
Zostera,  Potamogeton,  and  probably  all  submerged  monocoty- 
ledons.) 

II.  The  bundles  and  the  fundamental  tissue  are  plainly  differ- 
entiated ;    the  former  extending  almost  horizontally  from  the 
leaves  to  the  middle  of  the  cylinder,  then  curving  downwards, 
running   outwards,   and   finally   terminating   in   the   superficial 


is  assumed  that  the  leaves  alternate  with  precisely  one  half  divergence,  and  in- 
clude the  stem,  and  that  the  threads  stand  tangentially  perpendicular,  then  the 
actual  course  in  the  stem  will  be  shown  in  the  plan  of  a  radial  section  through 
the  median  thread  of  a  leaf  given  in  Fig.  109.  But  the  assumption  of  a  radi- 
ally perpendicular  course  is  valid  only  for  those  bundles  which  are  also  tangen- 
tially perpendicular.  As  was  first  observed  by  Meneghini,  admitted  afterwards 
by  Mohl  (Verm.  Schriften,  p.  160),  and  more  minutely  shown  by  Nageli,  each 
radially  curving  thread  runs  also  in  a  tangentially  oblique  direction,  and 
in  spiral  curves  which  are  proportionate  to  the  radial  curving.  Nageli  found 
the  median  thread  of  a  leaf  of  Chamaedorea  elatior,  Mart.,  for  example,  making 
1 J  revolutions  in  six  internodes  ;  in  the  sixth,  it  had  not,  in  its  outward  course, 
quite  reached  the  middle  point  between  the  centre  of  the  stem  and  the  inner 
surface  of  the  bark.  In  stems  with  very  short  internodes  and  closely  crowded 
bundles  the  spiral  curves  are  at  once  perceptible  in  the  cross-section,  being 
plainest  in  the  bundles  of  the  stem  of  Xanthorrhoea,  which  press  almost  hori- 
zontally towards  the  centre  of  the  stem,  this  peculiarity  giving  to  its  cross- 
section  the  strange  appearance  which  has  been  frequently  mentioned. 

"  Finally,  many  variations  from  that  course  of  a  thread  which  has  here  been 
described  as  typical  may  occur  ;  there  may  be  curvin^s  alternately  toward 
the  outside  and  the  inside,  etc.,  which  are  not  constant." 

1  Proceedings  of  American  Philosophical  Society,  1884,  p.  459. 


134  MINUTE  STRUCTURE  OF   THE  STEM. 

layers  of  the  central  cylinder.  (The  Mohl-Mirbel  Palm-Type, 
illustrated  by  Asparagus,  Iris,  Canna,  Aspidistra  (see  Fig.  103), 
Acorus,  Scirpus,  Zea,  etc.,  the 
underground  parts  of  Lilium, 
Tulipa,  etc.). 

III.  The  bundles  and  the 
fundamental  tissue  are  plainly 
differentiated  ;  the  bundles  run- 
ning downwards,  and  gradually 
converging  at  a  point  in  the 
middle  of  the  central  cylinder, 
here  blending  with  the  leaf- 
traces  of  older  leaves,  without 
again  curving  outwards.  (Ex- 
amples are  afforded  by  Trades- 
canti.-i.  the  parts  above  ground 
of  Lilium,  Tulipa,  etc.). 

385.  Guillard1  describes  six 
types  of  structure  in  the  stems  of 
monocot3Tledons  which  depend 
chiefly  upon  the  relations  of  a  central  zone  (called  "  interme- 
diate ")  to  the  fibro- vascular  bundles  in  the  remaining  portions  of 
the  stem.  The  classification  has  no  substantial  advantage  over 
that  of  Falkenberg. 

1  These  types  will  be  better  understood  after  some  peculiarities  in  the  ter- 
minology are  explained.  By  "  pith,"  in  monocotyledons,  Guillard  means  the 
central  region  of  parenchyma  ;  by  "intermediate  zone,"  the  active  zone  imme- 
diately surrounding  the  central  region  ;  by  "cortical  zone,"  the  zone  outside 
the  external  circle  of  bundles  and  the  products  of  the  intermediate  zone.  The 
six  types  are  the  following  :  — 

1st  Type.  No  intermediate  zone  between  the  pith  and  cortical  zone ; 
e.  g.,  Polygonatum  vulgare. 

2d  Type,     An  intermediate  zone  represented  by  different  tissues  :  — 

1.  Consisting  of  cauline  bundles  ;  e.  g.,  Iris  florentina. 

2.  Consisting  of  meristemiform  tissue  (that  is,  tissue  which  produced 

from  secondary  meristem  retains  the  shape  but  not  the  activity  of 
meristem)  ;  e.  g.,  Chamaedorea  elation 

3.  Consisting  of  a  fascicular  sheath  :  e.  g.,  Epipactis  palustris. 

4.  Consisting  of  the  three  foregoing  ;  e.  g.,  Acorus  Calamus. 

3d  Type.  A  single  external  zone  of  bundles,  with  a  potential  intermediate 
zone  ;  e.  g.,  Luzula  campestris. 

4th  Type.  Common  bundles  in  two  groups  :  one  at  the  centre  of  the  stem, 
the  other  forming  the  ordinary  circle,  separated  from  the  first  by  a  poten- 
tial intermediate  zone  ;  e.  g.,  Tradescantia  Virginica. 

FIG.  110.  Distribution  of  the  flbro-vascular  bundles  in  the  leaf-shaped  branch  of 
Ruscus  hypoglossum.  (Ettingshausen.) 


SECONDARY   STRUCTURE. 


135 


SECONDARY  STRUCTURE. 

386.  It  has  been  noticed  that  the  flbro-vascular  bundles  of 
monocotyledons  differ  from  those  of  dicot3-ledons  chiefly  in  the 
possession  by  the  latter  of  a  layer  of  merismatic  tissue  (cambium) 
between  the  cribrose  and  woody  portions.     The  stems  of  peren- 
nial dicotyledons  increase  in  thickness  from  year  to  year  chiefly 
by  the  annual  production  of  a  new  mass  of  wood  upon  the  in- 
side of  this  layer,  and  of  liber 

upon  the  outside ;  but  the  stems 
of  most  monocotyledons  have  no 
provision  for  annual  increase  in 
diameter.  Hence  it  is  convenient, 
in  spite  of  numerous  anomalies, 
to  consider  the  secondary  struc- 
ture of  the  stem  under  these  two 
heads. 

387.  Secondary     structure     of 
moiiocot)  ledouous  steins.      As  has 
been  already  observed,   the   pri- 
mary bundles  in  palms  run  from 
the  leaves  in  curves  of  long  ra- 
dius   until    they    again    approach 
the  surface  of  the  stem,  and  their 
fullest   development   is   found    in 
the  middle  part  of  their  course. 
While    a    cross-section    exhibits 
these  bundles  as  scattered  without 
much  order  in  a  mass  of  paren- 
chyma,  a  vertical   section  shows 
that  they  have  entered  the  stem 
at    different    heights    (since    the 

leaves  with  which  they  were  developed  were  at  different  points 
on  the  stem).  A  vertical  section  can  display  only  parts  of  most 
of  these  curved  bundles.  At  the  stem  of  a  palm  just  below  the 
crown  of  leaves  there  are  as  many  bundles  seen  in  a  cross-sec- 

5th  Type.  A  central  mass  of  secondary  tissue,  formed  from  central  meris- 
tem.  Intermediate  zone,  well  developed  ;  e.  </.,  Triglochin  maritimum. 

6th  Type.  Bundles  having  several  distinct  liber  elements;  e.  g.,  Tamus 
communis.  (Anatomie  de  la  tige  des  Monocotyledones,  Ann.  des  Sc. 
nat.,  ser.  6,  tome  v.,  1878,  p.  1.) 

FIG.  111.    A  diamond-shaped  mesh  of  primary  fascicles  intermingled  with  secondary 
fascicles  in  the  stem  of  an  Opuntia.    (Keinke. ) 


136  MINUTE   STRUCTUBE   OF   THE   STEM. 

tion  as  have  been  derived  from  the  leaves  at  that  point ;  and 
since  these  bundles  do  not  possess  a  cambium  layer,  the}-  have 
no  power  of  increasing  in  size.  The  only  changes  therefore  to 
be  looked  for  in  the  stem  of  a  palm  from  year  to  year  are  those 
in  the  ragged  exterior  from  which  the  leaves  fall,  and  the  pos- 
sible increase  in  firmness  of  the  individual  elements  of  the  older 
bundles.  The  stems  of  most  palms  are  as  thick  when  they  begin 
to  ascend  from  the  ground  as  they  will  afterwards  be,  their  bun- 
dles early  becoming  permanent  tissue  throughout. 

388.  The  presence  of  obscure  nodes  in  the  stem  may  com- 
plicate its  structure  somewhat  by  the  introduction  of  horizontal 
interlacing  bundles  ;  but  there  is  in  these  cases,  as  in  the  former, 
no  provision  for  increase  in  thickness. 

389.  In  some  monocotyledonous  stems  new  bundles  can  arise 
in  a  merismatic  layer  just  within  the  cortex,  and  therefore  cause 
an  increase  in  the  diameter  of  the  stem. 

A  similar  mode  of  increase  in  thickness  is  met  with  in  the 
stems  of  man}-  dicotyledons ;  as  those  of  Nyctaginacea?,  many 
Chenopodiacese  and  Amarantacese,  etc.  Secondary  bundles  are 
formed  in  a  merismatic  layer  outside  the  primary  bundles,  and 
in  contact  with  their  liber. 

390.  The  secondary  structure  of  normal  dicotyledonous  stems 
(see  369)  is  easily  understood  when  it  is  remembered  that  the 
cambium  of  their  primary  bundles  possesses  the  power  of  form- 
ing the  following  kinds  of  tissue :  a,  new  wood  on  the  outside 
of  that  which  was  last  produced  ;  6,  a  layer  of  new  liber ;  c,  fresh 
cambium  for  subsequent  activity ;  and  o?,  continuations  of  the 
medullar}'  rays. 

The  cambium  layer  in  the  stems  of  most  dicotyledons  is  com- 
posed of  extremely  delicate,  thin-walled  cells,  which  are  filled 
with  protoplasm  and  building  materials.  In  the  spring,  when 
the  bark  is  readily  stripped  from  the  wood,  this  layer  appears  as 
a  thin  film  of  mucilaginous  matter,  showing,  to  the  naked  eye,  no 
cellular  structure.  In  the  case  of  such  plants  as  the  maple, 
birch,  and  pine,  this  juicy  mass  possesses  a  very  sweet  taste, 
owing  to  the  large  amount  of  organizable  nutrient  matter  which 
it  contains. 

391.  The  cambium  layer  exposed  by  removal  of  the  bark  soon 
dies,  and  of  course  all  further  increase  in  diameter  is  impossible 
unless  the  wound  is  healed  in  some  way  (see  421). 

392.  The  growth  in  size  of  the  stems  of  normal  dicotyledons 
depends  therefore  upon  the  existence  and  activity  of  cambium 
cells  between  the  wood  and  bark.     The  juxtaposition  of  the 


INCREASE    IN    SIZE   OF   STEMS. 


137 


primary  bundles  brings  the  cambium  into  the  form  of  a  circle, 
sometimes  broken,  but  frequently  uninterrupted.  If  the  cam- 
bium circle  is  substantially  unbroken,  a  new  compact  ring  of  wood 
is  laid  upon  the  wood 

of  the  primary  bun-  B  A. 

die,  and  a  new  ring 
of  liber  forms  within 
the  older  liber.  This 
action  may  be  indefi- 
nitely repeated ;  and 
in  a  climate  where 
there  are  notable  dif- 
ferences either  in  tem- 
perature or  moisture 
between  the  seasons, 
the  concentric  circles 
are  records  of  the 
years. 

If  the  primary  bun- 
dles are  not  in  con- 
tact, the  new  wood 
added  }*ear  by  year 
simply  increases  the 
size  of  the  wedges  at 
their  outer  part. 

393.  New  bundles 
may  be  intercalated 
directly  between  those 
already  present,  and 
grow  in  much  the 
same  manner  as  the 
primary  ones ;  or  the}1 
may  arise  at  new  points  of  activity  and  produce  great  changes 
of  form.  In  the  same  way  tertiary  changes  and  those  of  a 
higher  order  may  follow  the  secondary  ones,  giving  rise  to  stems 
which  have  a  very  complicated  structure.  The  most  puzzling 


FIG.  112.  Diagrams  showing  the  secondary  increase  in  thickness  of  a  normal  dicoty- 
ledonous stem :  11,  cortex ;  p,  phloem  with  three  fascicles  of  hard-bast  fibres ;  x,  xylem ; 
M,  pith.  A  shows  only  primary  structure;  B  exhibits  formation  of  the  ring  of  cam- 
bium ;/c,  fascicular  cambium;  ic.  inter-fascicnlar  cambium;  f>,  l>,b.  fascicles  of  hard 
bast;  C,  at  the  end  of  the  year,  affer  the  formation  of  the  secondary  tibro- vascular  ring; 
p,  liber ;  fh,  secondary  wood  of  the  bundle;  ifj>,  inrer-fascieular  liber;  ifh,  inter-fas- 
cicular  secondary  wood;  the  entire  ring  is  subdivided  by  medullary  rays  of  different 
lengths.  (Sachs.) 


1-38        MINUTE  STRUCTURE  OF  THE  STEM. 

cases  can  generally  be  referred  to  eccentric  growth  of  some  one 
or  more  parts,  as  in  flattened  stems,  or  explained  by  the  intro- 
duction and  more  vigorous  growth  of  supernumerary  bundles. 

394.  Extraordinary  anomalies  are  afforded  by  the  lianes  of 
tropical  countries,  woody  climbers  with  distorted  stems.  They 
belong  chiefly  to  a  few  orders ;  namely,  Bignoniaceae,  Mal- 
pighiacese,  Menispermaceaj,  and  Aristolochiacese.  A  few  inter- 
esting cases  are  shown  in  the  accompanying  figures,  and  are 
sufficiently  explained  in  the  descriptive  letter-press. 


395.  Spring  wood  and  antnmn  wood.  The  secondary  wood  an- 
nually produced  in  a  temperate  climate  like  ours  exhibits  certain 
differences  between  the  inner  and  the  outer  portion  of  the  year's 


FIG  113.  Transverse  section  of  the  stem  of  a  liane  belonging  to  the  order  Malpighi- 
aeeae:  m,  pith;  b,  the  central  portion  of  the  wood,  arranged  in  concentric  layers  around 
the  pith.  (Duchartre.) 

FIG.  114.  Transverse  section  of  the  stem  of  a  liane  belonging  to  the  order  Malpighi- 
aceae :  m,  the  pith.  The  bark  follows  all  the  irregularities  of  the  wood.  ( Duchartre. ) 

FIG.  115.  Transverse  section  of  a  liane  belonging  to  the  order  Sapindacese:  b,  pri- 
mafy  woody  body  having  its  own  pith  m,  and  bark  e'c ;  b',  b',  b',  three  secondary  woody 
bodies  without  pith,  but  having  as  thick  a  bark  as  the  primary  body.  (Duchartre.) 

FIG.  1 16.  Transverse  sectio-i  of  the  stem  of  a  liane  belonging  to  the  order  Sapindaceae : 
b,  the  primary  or  central  woody  body  having  its  own  pith  m;  b',  b',  b',  b',  a  circle  of  un- 
equal secondary  woody  bodies;  b",  tertiary  woody  bodies.  (Duchartre.) 


ANNUAL  KINGS.  139 

ring.  That  which  is  produced  earliest  (spring  wood)  has  some- 
what larger  ducts  and  wood-cells  than  that  which  is  formed  later 
(autumn  wood) .  The  difference  is  not  very  striking  when  the 
wood  of  a  single  }7ear  is  examined,  for  the  diminution  in  size 
is  gradual  from  within  outwards  ;  but  if  the  autumn  wood  of  one 
3'ear  is  compared  with  the  spring  wood  in  the  next  ring,  the  dif- 
ference is  very  marked.  The  cause  of  the  difference  in  character 
between  the  earl}'  and  later  wood  formed  during  a  single  season 
is  supposed  to  be  the  greater  pressure  exerted  by  the  tense  bark 
in  autumn.  The  experimental  evidence  in  favor  of  this  view 
will  be  presented  in  the  chapter  on  "  Growth." 

396.  In  climates  where  there  is  no  marked  arrest  of  vegetative 
activity  during  the  whole  }rear,  for  instance,  in  that  of  the  equa- 
torial zone,   the  secondary  wood  seldom   presents  any  clearly 
defined  annual  rings.     In  the  wood  of  warm,  temperate  zones, 
however,  well-marked  annual  rings  are  not  uncommon. 

397.  It  has  long  been  known  that  in  temperate  climates  a  tree 
may  exceptionally  form  a  double  ring  in  a  single  year.     The 
cause  of  this  in  cases  which  have  been  carefully  examined  ap- 
pears to  be  :   (1)  a  partial  cessation  of  activity  owing  to  injury, 
followed  by  (2)  a  renewal  of  activit}*  in  the  same  season.     Thus 
an  elm  may  be  stripped  of  its  leaves  in  early  summer  and  suffer 
a  temporary  check ;    but  the  buds  already  formed  for  another 
year  develop  into  full  leaf  iu  a  short  time,  the  assimilative  activ- 
ity is  resumed,  and  two  rings  are  formed  as  a  result  of  this  ces- 
sation and  renewal.     Kny 1  has  found  this  to  be  the  case  with 
several  trees  which  had  been  deprived  of  their  foliage  at  the  end 
of  June.      Wilhelm  has  found  b}T  experiment  that  a  tolerably 
well-defined  double  ring  was  formed  in  Quercus  sessiliflora,  from 
which  he  removed  all  the  leaves  on  the  7th  of  June ;  while  in  a 
second  case,  where  the  foliage  was  removed  later  (July  10th), 
the  duplication  of  the  ring  was  not  apparent. 

398.  From  this  statement  it  would  appear  that  even  in  tem- 
perate climates,  where  there  is  a  prolonged  period  of  complete 
inactivity  due  to  the  cold,  the  number  of  rings  shown  in  the 
cross-section  of  a  stem  may  not  exactly  coincide  with  the  num- 
ber of  years  through  which  the  tree  has  lived.     But,  as  matter 
of  fact,  the  lines  of  limitation  in  the  intercalated  rings  are  so 
much  less  distinct  than  those  on  either  side,  that  the  two  lesser 
rings  would  be  counted  as  one,  and  therefore  be  credited  to  the 
growth  of  one  year  instead  of  two. 

1  Vcrhaudl.  d.  botau.  Vereins  der  Prov.,  Brandenburg,  1880. 
3  Child  :  Popular  Science  Monthly,  December,  1883, 


140  MINUTE   STRUCTURE   OF   THE   STEM. 

The  largest  number  of  rings  yet  reported  in  any  case  appears 
to  be  that  given  for  the  great  trees  of  California  ;  namely, 
" 2,100,  with  a  probability  that  others  considerablj-  exceed  this." 1 
Other  higher  numbers  of  rings  or  estimates  of  age  are,  however, 
given  in  some  works.2 

399.  That  it  is  unsafe  to  base  any  calculation  of  the  age  of  a 
tree  upon  its  diameter  follows  from  the  fact  that  its  growth  dur- 
ing one  year  differs  from  that  during  another  (see  400).   Even  the 
use  of  De  Candolle's  modification  of  Otto's  rule,3  which  is  per- 
haps the  best  }*et  given,  leads  to  erroneous  results.    The  method 
assumes  that  the  number  of  rings  averages  nearly  the  same  to 
an}-  given  unit  of  thickness  in  the  outer  as  in  the  inner  part  of 
the  stem.     Having  determined  the  number  of  rings  in  an  inch 
just  under  the  bark,  this  number  is  multiplied  by  the  radius  in 
order  to  obtain  the  whole.    For  example  :  Extract  from  opposite 
sides  of  a  tree  two  pieces  having  a  depth  of  two  inches  each. 
Suppose  the  number  of  rings  in  the  two-inch  piece  on  one  side 
to  be  20,  while  in  the  other  there  are  32,  the  average  per  inch 
will  be  13.     Deduct  twice  the  thickness  of  the  bark  from  the 
whole  diameter  of  the  tree,  to  obtain  the  diameter  of  the  wood 
in  inches,  and  multiply  one  half  of  the  diameter  by  13. 

400.  The  woody  rings  annually  formed  in  a  stem  differ  con- 
siderably in  size ;  a  narrow  ring  being  the  growth  of  a  cold 


1  S.  Watson,  in  Addendum  to  Botany  of  California. 

2  The  following  estimates  cited  by  De  Candolle   (Physiologic  Vegetale, 
p.  1007)  are  believed  to  range  altogether  too  high  :  — 

The  Linden  of  Neustadt,  in  Wiirtemberg,  1147  years. 

The  Oak  of  Bordza  (on  the  Baltic),  710  distinct  rings  counted  and  300  in- 
distinct rings  estimated  =  1010  years.  (By  Otto's  rule  this  would  be  1080 
years. ) 

The  Yew  of  Crow-Hurst  (Surrey),  measured  by  Evelyn  in  1660,  1458  years. 

The  Yew  of  Braburn  (Kent),  measured  by  Evelyn  in  1660,  and  said  by  him 
to  be  superannuated,  2880  years. 

The  estimate  given  by  De  Candolle,  of  the  age  of  trees  of  Adansonia  ( Bao 
bab);  namely,  6,000  years,  has  been  shown  by  Dr.  Gray  (North  American 
Review,  1844)  to  be  wholly  erroneous. 

3  Otto's  rule  is  thus  given  by  De  Candolle  :  Ascertain  the  diameter  at  the 
height  of  about  five  feet,  and  make  a  notch  at  the  same  point  on  the  circular 
surface,  to  count  a  certain  number  of  annual  layers  which  we  measure.     We 
then  find  the  annual  growth  of  those  trees  which  have  left  off  growing  in  height 
by  the  formula  lf^~!'7)  V,  and  of  those  which  continue  to  grow  in  height  by 
the  formula  7y~(^2rf)3  F;  D  being  the  diameter  of  tree  ;  V,  volume  of  same  ; 
d,  thickness  of  annual  layers  which  have  been  counted  ;  n,  the  number  of  these 
layers  (Physiologic  Vegetale,  p.  981  . 


SAP-WOOD   AND    HEAKT-WOOD.  141 

season,  a  broad  ring  of  a  warmer  one.  Their  width  varies  also 
in  the  same  species  in  different  localities :  thus,  in  Finns  sylves- 
tris,  grown  between  50°  and  60°  north  latitude,  in  Europe  (the 
space  occupied  by  the  British  Isles) ,  the  annual  laj-ers  are  very 
seldom  less  than  £  of  a  millimeter  in  thickness ;  while  in  the 
same  tree,  grown  far  north,  the  thickness  is  not  -^  of  a  milli- 
meter.1 The  width  varies  also  in  different  parts  of  the  same 
ring.  For  instance,  in  the  case  of  Pinus  sylvestris,  Bravais  and 
Mai-tins  found  the  two  opposite  radii  in  a  stem  to  have  the  ratio 
of  9  to  19,  the  side  having  the  greatest  thickness  being  that 
which  had  its  foliage  best  exposed  to  air  and  light.  The  eccen- 
tric growth  of  the  wood  of  branches  has  been  often  noted  ;  the 
longer  radii  are  those  on  the  lower  side. 

401.  Sap-wood  (Alburnum).      The  new  and  soft  wood  con- 
tains a  larger  proportion  of  soluble  organic  matters,  of  nitro- 
genous substances,  and,  when  fresh,  of  water,  than  the  older, 
harder  wood  lying  just  within.     The  "  sap  "  of  the  tree  is  found 
in  largest  amount  in  the  newer  wood.     The  name  alburnum  was 
given  to  the  sap-wood  by  the  early  histologists  on  account  of  its 
white  or  pale  color.     Contrasted  with  it,  but  not  always  very 
sharplv,  is  the  harder  substance,  Heart-wood,  or  Duramen.2    The 
latter  was  given  its  name  because  of  its  greater  hardness,  or 
durability.     Generally  there  is  some  distinction  in  color  between 
the  sap-wood  and  heart-wood,  owing  to  the  presence  of  peculiar 
coloring-matters  lodged  in  the  texture  of  the  latter.8 

402.  Color  of  wood.   The  deep  colors  which  characterize  man}- 
kinds  of  wood  are  contained  chiefly  in  the  walls  of  the  cells  and 
ducts.      In  Hsematoxylon   Campechianum    the    coloring- matter 
sometimes  occurs  also  in  crystals  inside  the  cells  themselves  or 
in  clefts  of  the  wood.    The  wood  of  Pterocarpus  santalinus  (Red 
Sanders-wood)  consists  of  libriform  cells  intermingled  with  small 
groups  of  very  large  ducts,  both  of  which  contain  the  rub}-  color- 
ing-matters in  large  amount.      Many  Berberidaceae,  Cladrastis 
tinctoria,  Cercis,  etc.,  have  yellow  coloring-matters  in  the  wood  ; 
in  Guaiacum  the  color  is  greenish ;  in  black  walnut,  brown ;  in 
ebony,  nearlv  black. 


1  Bravais  and  Martins :  Ann.  des  Sc.  nat.,  ser,  2  tome  xix.,  1843,  p.  129. 

2  The  word  Duramen  is  used  by  some  writers  to  denote  merely  that  heart- 
wood  which  has  become  very  dense  by  peculiar  infiltrations  (Saunersdorfer,  in 
Sitzungsber.  d.  k.  Akad.  Wien.,  1882). 

8  The  following  figures,  giving  the  proportion  of  sap-wood  to  the  entire  vol- 
ume ot  the  trunk,  are  from  Tred-rold  (Principles  of  Carpentry,  Section  X. ,  cited 
by  Rankine)  :  Chestnut,  0.1  ;  Oak,  0.294  ;  Scotch  Fir,  0.418. 


142  MINUTE   STRUCTURE   OF   THE   STEM. 

403.  It  may  be  here  mentioned  that  man}'  woods  have  charac- 
teristic odors  ;  for  instance,  sandal-wood,  violet-wood,  and  many 
of  the  coniferous  woods. 

404.  The  presence  of  resinous  matters  in  wood,  particularly 
when  these  are  evenhy  although  sparingly  distributed  through  the 
mass,  exerts  a  marked  effect  in  retarding  decay.    The  durability 
of  the  wood  of  Southern  Cypress,  even  when  exposed  to  the  joint 
action  of  the  warmth  and  moisture  of  a  greenhouse,  is  usually 
attributed  to  their  presence.     But  there  are  some  cases  of  great 
resistance  to  the  influences  producing  decay,  which  cannot  be 
referred  to  the  same  mode  of  protection ;  for  instance,  those  of 
Robinia  Pseudacacia  (or  common  "  Locust ")  and  Catalpa. 

405.  Various  processes  have  been  tried  for  destroying  the 
putrescible  matters  in  cells,  or  so  modifying  the  character  of 
the  cell-wall  that  the  wood  can  be  protected  against  decay. 

406.  The  oldest  known  method  of  preserving  wood  is  car- 
bonizing, or  charring,  by  which  those  constituents  of  the  wood 
specially  liable  to  decay  are  so  changed  as  to  be  no  longer  liable 
to  putrefaction.     The  wood-preserving  processes  known  as  Bur- 
nettizing  and  Kyanizing  have  for  their  object  the  coagulation  of 
protein  matters  in  wood-cells,  thus  retarding  if  not  preventing 
putrefaction. 

407.  In  Kyanizing,  a  solution  of  mercuric  chloride  is  forced 
into  the  texture  of  the  wood ;  but  the  cost  of  this  substance 
is  so  great,  that  it  has  led  to  a  general  abandonment  of  the 
process. 

408.  In  Burnettizing,  the  wood  is  impregnated  with  a  solution 
of  zinc  chloride  containing  about  fifty-five  per  cent  of  the  dry 
chloride.     This  is  forced  into  the  wood  under  pressure. 

409.  Another  process  —  creosoting  —  depends  upon  the  intro- 
duction into  the  wood  of  a  solution  of  impure  creosote,  a  pressure 
of  about  one  hundred  and  fifty  pounds  to  the  square  inch  being 
maintained  until  the  wood  has  absorbed  a  sufficient  amount  of 
the  antiseptic  liquid.     Some  of  the  antiseptic  matters  obtained 
by  a  rough  distillation  of  coal-tar  are  also  used  for  preserving 
wood. 

It  is  an  interesting  fact  that  even  wood  which  in  the  air 
is  specially  liable  to  decay  can  be  preserved  for  a  long  time  if 
deeply  submerged  in  water. 

410.  There  is  an  appreciable  difference,  especially  in  length, 
between  the  wood-cells  of  the  earlier  annual  rings  and  those 
which  succeed  them  ;  and  Sanio  has  shown  that  an  increase  of 
length  of  the  cells  occurs  up  to  a  certain  period  of  growth,  when 


SIZE   OF   WOOD-CELLS.  143 

an  average  appears  to  be  established.  This  fact  is  illustrated 
by  the  following  table,  based  on  measurements  of  tracheids  of 
Pinus  sylvestris.1 

Number  of  the  annual  Medium  length  of  the  Medium  width  of  the 

ring.  tracheids.  trachei'ds. 

1 95  mm.  .017  mm. 

17 2.74 

19 3.13 

31 3.69 

37 3.87 

38 3.91 

39 4.00 

40 4.04 

43 4.09 

45 4.21 

46 4.21 

72 4.21  .032mm. 

From  this  table  it  is  seen  that  the  increase  can  be  traced  up  to 
the  forty-fifth  year,  but  that  from  that  time  on,  the  tracheids  in 
one  ring  have  the  same  length  as  those  in  the  next.  Those  in 
the  forty-fifth  annual  ring  have  an  average  length  of  about  five 
times  that  of  those  in  the  first.  In  the  wood  of  oak,  the  libri- 
form  cells  exhibited  the  greatest  difference  in  length.  Thus 
Sanio  found  that  in  a  stem  of  Quercus  pedunculata,  with  130 
rings,  the  medium  length  of  these  elements  in  the  ring  of  the 
first  year  was  .42  mm.,  and  in  the  three  outer  rings  1.22  mm. 
Tracheids  in  the  same  rings  measured,  however,  only  .39  mm. 
and  .72  mm.  respectively.  With  this  increment  in  the  length  of 
wood  elements  in  successive  rings,  Haberlandt  associates  a  fact 
noticed  by  Alexander  Braun  ; 2  namely,  that  the  wood  elements 
in  some  stems  and  branches  stand  not  parallel  with  the  axis,  but 

1  Ueber  die  Grosse  der  Holzzellen  bei  der  gemeinen  Kiefer,  Prings.  Jahrb., 
viii.  409. 

2  Ueber  den  schiefen  Verlauf  der  Holzfaser,   und  die  dadurch   bedingte 
Drehung  der  Baume,  Berlin,  1854. 

It  is  proper  to  refer  at  this  point  to  an  instructive  paper  by  Abromeit 
upon  the  histology  of  the  oaks,  in  which  the  most  marked  characters  of  the 
North  American  species  are  fully  treated  (Pringsheim's  Jahrb.,  1884,  p.  209). 
According  to  Abromeit,  the  oaks  can  be  plainly  classified  as  follows :  — 
I.   With  wide  well-marked  medullary  rays. 

A.    The  annual  rings  distinctly  defined  by  the  concentric  circles  of  the 
larger  ducts  of  the  spring  wood,  and  seen  by  the  naked  eye.     The 
smaller  ducts  are  arranged  in  radial  rows  in  the  autumn  wood. 
a.    With  thin-walled  ducts. 

a.  The  radial  rows  of  small  ducts  touch  each  other  tangentially  : 
Quercus  lyrata,  alba,  Durandii,  stellata,  macrocarpa,  Wislizeni 
Prinus,  Garryana,  bicolor  (var.  Michauxii). 


144  MINUTE   STRUCTURE   OF   THE   STEM. 

somewhat  oblique  thereto.  The  degree  of  obliquity  is  generally 
from  4°  to  5°,  but  it  is  sometimes  much  higher  than  this  ;  for 
instance,  10°  to  20°  in  horse-chestnut,  30°  in  Syriuga  vulgaris 
(Lilac),  40°  in  Sorbus  aucuparia,  and  45°  in  Puuica  Granatum. 
411.  Density  of  wood.  Owing  to  its  greater  firmness  and 
smaller  amount  of  putrescible  substances,  heart-wood  is  economi- 
cally of  far  greater  value  than  sap-wood ;  and  hence  nearly  all 
determinations  of  density,  strength,  etc.,  are  made  upon  it, 

/3.  The  radial  rows  of  the  smaller  ducts  are  relatively  narrow  and 
for  the  most  part  isolated  tangentially  :  Quercus  bicolor,  ses- 
silitlunt,  Iberica,  grosseserrata,  castaneifolia,  pedunculata, 
Thomasii,  undulata  (var.  grisea),  Mongolica,  macranthera, 
heterophylla. 

•y.    The  radial  rows  of  the  smaller  ducts  are  very  narrow,  and  the 
ducts  differ  somewhat  in  width.     The  large  ducts  are  in  groups 
in  the  concentric  circles  :  Quercus  lobata. 
b.    With  thick-walled  ducts. 

a.  The  large  ducts  in  the  concentric  circles  are  indistinctly  grouped, 
while  the  small  ducts  are  crowded  in  narrow  radial  rows  : 
Quercus  rubra  and  the  var.  ?  Texana.  Quercus  tinctoria. 
/3.  Large  ducts,  as  in  the  previous  group.  The  radial  lines  of  the 
smaller  ducts  wide,  and  the  ducts  themselves  visible  to  the 
naked  eye  :  Quercus  imbricaria,  hypoleuca,  laurifolia,  Kelloggii, 
palustris,  talcata,  Catesbaei,  aquatica,  nigra. 

7.  With  distinct  radial  grouping  in  the  circles  of  the  larger  ducts  of 
the  spring  wood.  The  radial  rows  of  smaller  ducts  narrow  and 
straight.  The  small  ducts  visible  to  the  naked  eye  :  Quercus 
Cerris,  serrata,  Phellos,  coccinea. 

B.  Having  thick-walled  ducts  of  one  kind,  and  these  arranged  in  radial 
rows  or  groups.  The  annual  rings  are  not  distinct  to  the  naked  eye, 
and  are  denned  chiefly  by  the  thick-walled  wood-cells  of  the  outer 
layers  of  the  autumn  wood.  They  are  easily  made  out  under  the 
microscope. 

a.    The  radial  rows  of  ducts  are  for  the  most  part  wide  :   Quercus 

virens,  oblongifolia,  chrysolepis,  rngosa,  Ilex,  coccifera,  Calli- 

prinos,    lanuginosa,  paucilammellosa,    glabra,   Burgeri,   gilva, 

thalassica. 

/3.    Radial  rows  of  ducts  mostly  narrow  :  Quercus  Suber,  agrifolia, 

glauca. 

II.  The  wide  medullary  rays  appear  under  the  microscope  to  be  somewhat 
interrupted  by  wood-cells,  so  as  to  appear  like  groups  of  narrower 
rays :  Quercus  dilatata. 

The  principal  kinds  of  wood-cells  in  oaks,  according  to  the  nomenclature  of 
Abromeit,  are :  first,  the  "  pointed,"  of  which  there  are  two  varieties,  the  septate 
and  the  unseptate  ;  and,  second,  the  "blunt,"  which  are  of  comparatively  wide 
caliber,  and  have  thin  walls.  The  length  of  the  pointed  cells  in  an  average  of 
171  measurements  was  found  to  be  1.224  mm.  ;  that  of  the  blunt  cells  only 
.1  mm.  Besides  these  two  chief  kinds,  there  are  transitional  forms  of  every 
sort. 


DENSITY   OF   WOOD. 


145 


rather  than  upon  the  latter.  The  lightest  wood  is  probably  the 
so-called  "  cork- wood"  of  the  West  indies  (Ochromu  Lagopus), 
with  a  specific  gravity  of  .25  ;  the  heaviest  is  Condalia  ferrea, 
specific  gravity  1.302.1  The  specific  gravity  of  pure  cellulose  is 
given  by  authors  variously  as  1.25  to  1.52  ; 2  hence  the  figures 
noted  above  for  the  extremes  of  wood-density  show  indirectly  the 
degree  of  buo3*ancy  imparted  by  the  air  entangled  in  the  tissues.3 
412.  Wood-fibre  used  for  paper-pulp.  The  longer  wood-cells 
of  many  common  ligneous  plants  can  be  profitably  separated 


1  Tenth  Census  of  the  United  States,  vol.  ix.,  p.  272. 

2  Ebermayer  :  Chemie  der  Pflanzen,  1882,  p.  164.     Husemann  and  Hilger: 
Die  Pflanzenstoffe,  1882,  p.  108. 

8  The  following  determinations  were  made  under  the  direction  of  Professor 
C.  S.  Sargent,  for  the  Tenth  United  States  Census. 


Botanical  name. 

Common  name. 

Region. 

4 

Si 

Sequoia  gi<;antea. 
Pinus  Stroluis. 

Big  Tree. 
White  Pine. 

California. 
North  Atlantic. 

0.2882 
0.3854 

18.20 
24.02 

Tsuga  Canailensis. 

Hemlock. 

North  Atlantic. 

0.4239 

2642 

Liriodendron    Tulipi- 

Whitewood. 

Atlantic. 

0.4230 

26.36 

fera. 

Taxodium  distichum. 
Castam-a  v  u  Igaris,  var. 

Cypress. 
Chestnut. 

South  Atlantic. 
Atlantic. 

0.4543 
0.4504 

27.65 
28.07 

Americana. 

Abies  nigra. 
Populus  grandidentata 

Black  Spruce. 
Poplar. 

North  Atlantic. 
North  Atlantic. 

0.4584 
0.4632 

2857 

28.87 

Pinus  resinosa. 

Norway  Pine. 

North  Atlantic. 

0.4854 

3025 

Pinus  rigid*. 

Pitch  Pine. 

Atlantic  Coast. 

0.5151 

32.10 

Acer  dasycarpum. 

Silver  Maple. 

Atlantic. 

0.5269 

3284 

Pynw  Americana 

Mountain-Ash. 

Atlantic. 

0.5451 

3397 

Betula  nigra. 

Red  Birch. 

Atlantic. 

0.5762 

3591 

Platanus  occidentalis. 

Sycamore,  Button  wood 

Atlantic. 

0.5678 

35.38 

Juglans  nigra. 

Black  Walnut. 

Atlantic. 

0.6115 

38.11 

Larix  Americana. 

Larch. 

North  Atlantic. 

0.6236 

38.86 

Ulnius  Americana. 

White  Elm. 

Atlantic. 

0.0506 

40.54 

Fraxinus  Americana 

White  Ash. 

Atlantic. 

0.6543 

4077 

Quercus  rubra. 

Red  Oak. 

Atlantic. 

0.6540 

40.75 

Acer  saecharinum. 

Sugar  Maple. 

Atlantic. 

0.6912 

43.08 

Fagus  ferruginea. 

Belch. 

Atlantic. 

0.6883 

4289 

Quercus  alba. 

White  Oak. 

Atlantic. 

0.7470 

4635 

Betula  lenta 

Cherry-Birch. 

Atlantic. 

0.7617 

47.47 

Quercus  virens. 

Live  Oak. 

South  Atlantic. 

0.9501 

59.21 

Guaiacum  sanctum. 

Lignum  Vitse. 

Semi-tropical  Florida. 

1.1432 

71.24 

The  specimens  used  in  the  above  determinations  by  Mr.  S.  P.  Sharpies  were 
dried  at  a  temperature  of  100°  C.  until  they  ceased  to  lose  weight,  when  the 
specific  gravities  were  obtained  by  measurement  with  micrometer  calipers  and 
calculation  from  the  weights  of  the  specimens. 

For  the  purpose  of  utilizing  histological  features  in  the  identification  of 
woods,  classiticatory  tables  have  been  prepared  by  many  authors.  One  of  the 
most  useful  of  these  is  given  in  Schacht's  work,  Die  Pflanzenzelle,  in  which 
the  different  wood-cells  of  Conifene  are  described,  in  order  to  aid  in  the  recog- 
nition of  the  genera.  Another  is  de  Bary's  ( Vergleichende  Anatomie.  p.  509, 
10 


146  MINUTE   STRUCTURE  OP  THE   STEM. 

from  each  other  by  mechanical  or  chemical  means  for  use  in  the 
manufacture  of  paper-pulp.  The  woods  which  appear  to  have 

translated  in  Sachs's  Text-book,  2d  Eng.  ed.,  p.  651),  in  which  the  structural 
characters  of  many  kinds  of  wood  are  given.  The  table  will  be  found  con- 
venient for  reference. 

1.  Wood  consisting  only  of  trachei'ds  with  bordered  pits  :  — 

Winterete  (Drimys  Winteri,  Tasmannia  aromatica  ;  also  Trochodendron 
aralioides)  :  (Conifers). 

2.  Wood  consisting  of  vessels,  tracheiids,  parenchyma,  and  intermediate  cells  ; 

that  is,  substitute  or  replacing  cells  or  fibres  (ersatzfasern)  :  — 

a.  With  no  intermediate  cells  ;  Ilex  aquifolium,  Staphylea  pinnata,  Rosa 

canina,  Crataegus  monogyna,  Pyrus  communis,  Spiraea  opulifolia, 
Camellia,  etc. 

b.  With  no  parenchyma  ;  Porlieria. 

c.  With  both  parenchyma  and  intermediate  cells ;  Jasminum  revolutum, 

Kerria,  Potentilla  fruticosa,  Casuarina  equisetifolia  and  torulosa, 
Aristolochia  Sipho,  etc. 

3.  Wood  consisting  of  vessels,  trachei'ds,  fibres,  parenchyma,  and  intermediate 

cells  :  - 

a.  With  no  intermediate  cells  ;  fibres  unseptate  ;  e.  g.,  Sambucus  nigra 

and  racemosa,  Acer  platanoides,  Pseudoplatanus,  and  campestris. 

b.  With  both  parenchyma  and  intermediate  cells  ;  fibres  unseptate  ;  Ber- 

beris  vulgaris,  Mahonia  ;  (Ephedra). 

c.  With  no  intermediate  cells ;    fibres  septate  and  unseptate  ;   Punica, 

Euonymus  latifolius  and  Europaeus,  Celastrus  scandens,  Vitis  vini- 
fera,  Fuchsia  globosa,  Centradenia  grand  ifolia,  Hedera  Helix,  etc. 

d.  With  all  four  kinds  of  cells  ;  Miihlenbeckia  complexa,  Ficus. 

4.  Wood  consisting  of  vessels,  tracheids,  fibres,  parenchyma,  and  intermediate 

cells.    This  is  the  most  common,  and  may  be  taken  as  the  typical  structure: 

a.  With  no  intermediate  cells  ;  Sparmannia  Africana,  Calycanthus,  Rham- 

nus  catharticus,  Ribes  rubrum,  Quercus,  Castanea,  Carpinus  sp., 
Amygdalese,  Melaleuca,  Callistemon  sp.,  etc. 

b.  With  no  parenchyma  ;  Caragana  arborescens. 

c.  With  both  kinds  of  cells  ;  most  foliage-trees  and  shrubs;  e.  g.,  Salix, 

Populus  sp.,  Liriodendron,  Magnolia  acuminata,  Alnus  glntinosa, 
Betula  alba,  Juglans  regia,  Nerium,  Tilia,  Hakea  suaveolens,  Ailan- 
thus,  Robinia,  Gleditschia  sp.,  Ulex  Europaeus,  etc. 

5.  Wood  consisting  of  vessels,  fibres,  parenchyma,  and  intermediate  cells  :  — 

a.  With  no  parenchyma  ;  Viscum  album. 

b.  With  no  intermediate  cells  ;  Avicennia. 

c.  With  both  kinds  of  cells  ;  Fraxinus  excelsior,  Ornus,  Citrus  medica, 

Platanus,  etc. 

6.  Wood  consisting  of  vessels,  fibres,  and  parenchyma  :  — 

Cheiranthus  Cheiri,  Begonia.     Also  many  Crassulacese  and  Caryophyl- 
lacese. 

7.  Wood  consisting  of  vessels,  fibres,  parenchyma,  and  true  woody-fibres  :  — 

Colens  Macraei,  Eugenia  australis,  Hydrangea  hortensis. 

8.  Wood  consisting  of  vessels,  tracheids,  woody  fibres,  septate  fibres,  paren- 

chyma, and  intermediate  cells  :  — 

Ceratonia  siliqua,  Bignonia  capreolata  ;  it  is,  however,  still  doubtful  if 
true  woody-fibres  are  present. 


SECONDARY   LIBER.  147 

been  most  extensively  employed  up  to  the  present  time  are  some 
of  the  species  of  Abies,  Betula,  Populus,  Tilia,  and  Liriodendron 
Tulipifera  (in  the  United  States  sometimes  called  "Poplar"). 
The  chemical  processes  depend  (1)  upon  the  solvent  power  of 
caustic  soda  under  pressure,  and  with  heat,  upon  the  so-called 
intercellular  substance  which  unites  the  cells,  or  (2)  upon  the 
similar  power  of  a  sulphite,  preferably  maguesic,  also  under 
pressure  and  with  heat. 

413.  Bark.     A,  Secondary  liber.     Each  yearly  addition  to  the 
inner  surface  of  the  bark  is  seldom  plainly  distinguishable  from 
those  which  have  preceded  it,  and  hence  we  cannot  determine 
positively  the  age  of  an  old  tree  by  the  layers  of  its  inner  bark. 
The  bast-fibres  of  a  single  year  often  cling  together  in  a  strik- 
ing manner,  forming  bands  or  strips  of  considerable  strength, 
and  in  a  few  cases,  notably  that  of  Daphne  Lagetta,  there  are 
fine  meshes  between  the  fibres,  so  that  the  inner  bark  seems  to 
be  composed  of  layers  of  delicate  lace. 

A  piece  of  thick  bark  of  linden  macerated  for  a  while  in  water 
becomes  so  softened  that  the  younger  portion  of  the  inner  bark 
can  be  easily  separated  into  the  annual  layers.  Strips  of  the 
coherent  fibres  form  the  Russia  matting  of  commerce.  The 
strips  often  measure  2-3  meters  in  length,  2-5  cm.  in  width, 
and  .04-  .08  mm.  in  thickness.  Scattered  among  the  individual 
hard-bast  fibres  there  are  many  parenchyma  cells,  some  of  which 
plainly  belong  to  the  medullary  rays,  and  others  to  the  fibro- 
vascular  bundles. 

414.  The  bast-fibres,  in  a  few  instances,  instead  of  being  re- 
tained upon  the  stem  for  an  indefinite  period,  are  separated  early, 
leaving  the  newer  bast  exposed.      This  is  the  case  with  some  of 
our  species  of  Vitis,  in  which  the  bast  becomes  detached  in  the 
form  of  long,  loose  shreds  after  the  first  year. 

415.  The  crystals  found  in  bast  are  very  abundant.     They 
are  chiefly  monoclinic,  and   occur   both  singly  —  arranged   in 
rows  —  and  in  clusters.1 

416.  The  appearance  and  distribution  of  the  fibres  of  bast 

1  De  Bary  gives  the  following  list,  taken  chiefly  from  Sanio  :  — 

Clusters  of  crystals  in  bast  of  Juglans  regia,  Rhus  typhina,  Viburnum  Oxy- 
coccus,  V.  Lantaua,  Primus  Padus,  Punica  Granatum,  Ptelea  trifoliata,  Ribes 
nigrum,  Lonicera  Tatarica. 

Single  monoclinic  crystals  in  bast  of  species  of  Acer,  and  the  Pomacese, 
Robinia,  Cladrastis,  Ulmus  campestris,  Berberis,  etc. 

Single  monoclinic  crystals  and  clusters  in  bast  of  Quercus,  Celtis,  ^Esculus 
Hippocastanum,  Hamamelis  Virginica,  Morus,  Salix,  Fagus,  Populus,  Car- 
pinus,  Betula,  Tilia,  etc. 


148  MINUTE  STRUCTURE  off  THE  STEM. 

are  so  characteristic  in  certain  kinds  of  bark  that  they  may  be 
used  for  identification.     An  example  is  given  below.1 

417.  B,  Cork,  which  has  already  been  described  in  part  in 
Chapter  II.,  plays  a  very  important  part  in  the  structure  of  older 
bark.  Its  relations  to  the  cells  which  produce  it,  and  to  the 
epidermis  which  it  displaces  at  an  early  period  of  its  growth,  will 
be  plain  from  an  examination  of  Fig.  117.  In  its  production 
there  are  periodic  arrests  of  activity  just  as  in  the  case  of  wood, 
and  hence  in  cork-tissue  of  firm  texture  it  is  possible  to  detect 
the  lines  of  annual  demarcation.  When  the  cork  of  the  cork- 
oak  has  reached  a  merchantable  thickness  (usually  in  ten  to  fifteen 
years),  it  is  removed  down  to  the  phellogen,  or  cork  cambium, 
and  from  this  tissue  new  growths  begin.8 

1  "The  liber  is  traversed  by  medullary  rays,  which  in  cinchona  are  mostly 
very  obvious,  and  project  more  or  less  distinctly  into  the  middle  cortical  tissue. 
The  liber  is  separated  by  the  medullary  rays  into  wedges,  which  are  constituted 
of  a  parenchymatous  part,  and  of  yellow  or  orange  fibres.     The  number,  color, 
shape,  and  size,  but  chiefly  the  arrangement  of  these  fibres,  confer  a  certain 
character  common  to  all  the  barks  of  the  group  under  consideration. 

"  The  liber- fibres  are  elongated  and  bluntly  pointed  at  their  ends,  but  never 
branched,  mostly  spindle-shaped,  straight,  or  slightly  curved,  and  not  exceed- 
ing in  length  3  mm.  They  are  consequently  of  a  simpler  structure  than  the 
analogous  cells  of  most  other  officinal  barks.  They  are  about  J  to  J  mm. 
thick,  their  transverse  section  exhibiting  a  quadrangular  rather  than  a  circu- 
lar outline.  Their  walls  are  strongly  thickened  by  numerous  secondary  depos- 
its, the  cavity  being  reduced  to  a  narrow  cleft,  a  structure  which  explains 
the  brittleness  of  the  fibres.  The  liber-fibres  are  either  irregularly  scattered 
in  the  liber-rays,  or  they  form  radial  lines  transversely  intersected  by  narrow 
strips  of  parenchyma,  or  they  are  densely  packed  in  short  bundles.  It  is  a 
peculiarity  of  cinchona  barks  that  these  bundles  consist  always  of  a  few  fibres 
(three  to  five  or  seven),  whereas  in  many  other  barks  (as  cinnamon)  analogous 
bundles  are  made  up  of  a  large  number  of  fibres.  Barks  provided  with  long 
bundles  of  the  latter  kind  acquire  therefrom  a  very  fibrous  fracture,  whilst 
cinchona  barks,  from  their  short  and  simple  fibres,  exhibit  a  short  fracture. 
It  is  rather  granular  in  Calisaya  bark,  in  which  the  fibres  are  almost  isolated 
by  parenchymatous  tissue.  In  the  bark  of  C.  scrobiculata  a  somewhat  short 
fibrous  fracture  is  due  to  the  arrangement  of  the  fibres  in  radial  rows.  In 
C.  pubescens  the  fibres  are  in  short  bundles,  and  produce  a  rather  woody  frac- 
ture" (Fluckiger  and  Hanbury,  Pharmacographia,  p.  317). 

2  As  noticed  in  246,  the  inner  layer  of  cork-meristem  may  give  rise  to  paren- 
chyma cells  containing  chlorophyll.     Of  these  cells  Sanio  says  :  "They  never 
become  cork-cells,  but  are  truly  parenchymatous  ;  they  are  filled  with  chloro- 
phyll, starch,  and  sometimes  with  crystals.     They  never  become  lignified,  but 
the  wall  remains  as  unchanged  cellulose,  and,  in  short,  they  are  true  cortical 
cells.     Since,  then,  they  owe  their  origin  to  the  activity  of  the  cork-meristem, 
but  behave  throughout  their  whole  subsequent  development  precisely  like  the 
cells  of  the  cortex,  they  may  be  called  cork-cortex  cells.     When  they  form  a 
distinctly  defined  layer,  the  term  Phelloderm  is  appropriate "  (Pringsheim's 
Jahrb.,  1860,  p.  47). 


BARK. 


149 


418.  In  some  plants,  notably  the  birch,  papery  layers  exfo- 
liate from  time  to  time,  while  in  some  other  plants,  e.  g.,  the 
shag-bark  hickory,  large  strips  of  irregular  form  and  thickness 
are 'detached.    Owing  to  the  mode  of  their  formation,  such  sepa- 
rated pieces  may  contain  very  heterogeneous  elements.   Of  them 
Sachs   says:1    "  Not   un- 

frequently  the  formation 
of  cork  penetrates  much 
deeper  [than  the  peri- 
derm]  :  lamellae  of  cork 
arise  deep  within  the  stem 
as  it  increases  in  thick- 
ness ;  parts  of  the  funda- 
mental tissue  and  of  the 
fibro-vascular  bundles,  or 
of  the  tissue  which  after- 
wards proceeds  from  them, 
become,  as  it  were,  cut 
out  by  lamellae  of  cork. 
Since  everything  which 
lies  outside  such  a  struc- 
ture dies  and  dries  up,  a 
peripheral  layer  of  dried 
tissue  collects,  which  is 
very  various  in  its  form 
and  origin.  This  struc- 
ture, abundant  in  Conif- 
erae  and  in  mam7  dicoty- 
ledonous trees,  is  the  bark,  the  most  complicated  epidermal 
structure  in  the  vegetable  kingdom." 

419.  Injuries  of  the  stem.     The  stem,  especialty  in  the  case 
of  plants  living  many  years,  is  particularly  liable  to  injuries,  the 
most  frequent  of  which  are  of  course  the  wounds  left  by  the  fall- 
ing of  the  lower  limbs.    It  is  proper  to  treat  here  of  the  natural 
repair  of  such  injuries. 

420.  When  any  part  of  a  plant  suffers  serious  mechanical 
injury  by  which  the  deeper  tissues  are  exposed,  the  surface  of 


1  Text-book,  2d  Eng.  ed.,  1882,  p.  95. 

FIG.  117.  Formation  of  cork  in  a  branch  of  Ribes  nigrnm,  one  year  old ;  part  of  a 
transverse  section;  e,  epidermis;  h,  hair;  b,  bast-cells;  pr,  cortical  parenchyma  dis- 
torted by  the  increase  in  the  thickness  of  the  branch ;  K,  total  product  of  the  phellogen  e  ; 
k,  the  cork-cells  radially  in  rows,  formed  from  c  in  centrifugal  order;  pd,  phelloderm 
(parenchyma  containing  chlorophyll  formed  centripetally  from  c).  (Sachs.) 


150  MINUTE   STRUCTURE   OF  THE   STEM. 

the  wound  exhales  moisture  very  rapidly,  and  under  ordinary 
circumstances,  except  in  spring,  soon  becomes  dry.  As  Hartig1 
has  shown,  the  dr}'ing  of  the  exposed  tissues  is  fatal  to  their 
component  cells,  and  the  organic  contents  speedily  undergo 
chemical  decomposition.  The  products  of  this  decomposition 
have  been  further  shown  by  him  to  be  fatal  to  neighboring  cells, 
and  under  certain  conditions  the  mischief  may  progress  to  an 
irreparable  extent.  But  usually  there  is  an  arrest  of  the  de- 
structive action  either  from  lack  of  the  free  oxygen  necessary  for 
the  putrefactive  process,  or  by  the  protection  afforded  by  tissues 
for  repair.  Wounds  in  resinous  trees  are  measurably  hindered 
from  effecting  much  damage,  owing  to  the  exudation  of  liquid 
resins  which  exclude  air. 

421.  The  smaller  wounds  of  a  plant  are  generally  healed  b}T 
cork  or  by  callus.     1.  By  cork.     The  superficial  layer  of  cells  at 
the  surface  of  the  wound  is  destroyed  by  the  injury,  and  dries 
at  once.     In  soft  tissues  the  layer  just  below  this  immediate!}' 
becomes  merismatic,  and  behaves  precisely  like  normal  cork- 
meristem,  covering  the  entire  wound  with  a  grayish  or  brownish 
film,  which  is  in  unbroken  connection  with  the  edges  of  the 
wound.     Extreme  dryness  of  the  air,  or,  on  the  other  hand,  ex- 
treme humidity,  hinders  repair  by  cork.     2.  B}'  callus.     This  is 
best  studied  in  leaves  and  in  "cuttings."     When  a  young,  juicy 
leaf  is  wounded  by  an  incision,  some  of  the  cells  at  the  exposed 
surface  may  give  rise  to  elongated  sac-like  bodies,  which  fill  up 
the  greater  part  of  the  injured  cavity,  and,  according  to  Frank,'2 
serve  as  a  new  epidermis.     Or  small  cells  in  close  apposition 
may  be  at  once  formed,  and  completely  protect  the  tissue  below. 
In  "  cuttings"  the  callus  immediately  forms  a  swelling  near  the 
wound.     A  portion  of  the  callus  ma}'  by  continued  cell-division 
extend  over  the  cut  end,  ever}'where  bounded  on  its  exposed 
surface  by  a  cork  layer.     Activity  of  the  cells  in  the  callus  and 
around  the  fibro-vascular  bundles  soon  gives  rise  to  new  parts, 
for  instance,  roots. 

422.  It  often  happens  under  favorable  conditions  that  a  large 
mass8  of  tissue  is  gradually  formed  around,  and  finally  over,  a 
large  injured  surface. 

1  Zersetzungserscheinungen  des  Holzes,  Berlin,  1878.     (Quoted  by  Frank.) 

2  Die  Pflanzenkrankheiten,  1879. 

8  Usually  when  a  branch  dies  it  remains  attached  for  a  while  to  the  stem ; 
and  no  wound  is  in  fact  caused  until  the  slow  desiccation  of  the  deeper  tissues 
has  gone  on  to  a  considerable  extent,  and  without  exposure  to  atmospheric 
air  or  outside  moisture.  When  the  branch  at  last  falls  off,  the  tissues  around 


LENTICELS.  151 

423.  Lenticels  are  peculiar  breaks  in  the  continuity  of  the 
periderm  of  dicotyledons.  In  some  cases  they  can  be  detected 
under  minute  elevations  of  the  epidermis  of  the  first  year,  which 
split  open  either  at  the  end  of  that  season  or  during  the  next, 
forming  a  rift  running  lengthwise  of  the  stem.  Through  this  cleft 


underlying  tissues  appear,  protruding  in  an  irregular  manner, 
the  whole  structure  constituting  a  lenticel.  According  to  Stahl,1 
there  are  two  types  of  lenticels  :  1 .  Those  with  loose  cells  in  the 
rift,  alternating  with  denser  lines  of  cells.  This  is  the  most 
common  type,  good  examples  being  afforded  by  Alnus,  Prunus, 
^Esculus,  etc.  2.  Those  with  closely  united  cells  and  with  no 
alternating  denser  lines.  Illustrations  can  be  found  in  Sam- 
bucus  (see  Fig.  118),  Salix,  Cornus,  etc.  The  same  authority 
states  that  in  winter  both  of  these  kinds  form  an  impervious 
periderm-like  layer.  It  appears  from  Stahl's  examination  that 
in  their  complete  and  open  state  they  aid  in  the  exchange  of 

§  gases  between  the  interior  and  exterior  of  the  stem.  Klebahn 2 
its  base  are  in  a  healthy  condition,  while  the  internal  shaft  of  wood  is  dry,  and 
not  liable  to  undergo  rapid  decay.  The  formation  of  a  separative  mass  over 
the  wood  can  therefore  go  on  to  completion. 

1  Bot.  Zeit.,  1873.  Compare  Haberlandt :  Sitz.  d.  k.  Akad.  Wien,  Band 
Ixxii.  Abth.  i.,  1875. 

a  Berichte  der  deutschen  botanischen  Gesellschaft,  1883,  p.  119. 

PIG.  118.  Section  through  a  lenticel  in  the  periderm  of  Sambucus  nigra:  k,  peri- 
derm  ;  r,  primary  cortex ;  v,  ineristem,  above  which  are  the  cells  therefrom  produced ; 
6,  liber.  (Stahl.) 


152  MINUTE   STRUCTURE  OF  THE   STEM. 

has  lately  shown  that  even  in  stems  with  the  periderra  free  from 
lenticels,  provision  for  exchange  of  gases  is  secured  by  certain 
intercellular  spaces  at  or  near  the  points  where  the  medullary 
rays  come  to  the  periphery  of  the  stem. 

424.  Grafting.     If  the  cambium  tissue  of  a  young  shoot  is 
retained  for  a  time  in  close  apposition  with  that  of  a  nearly 
related  plant,  union  of  the  two  parts  may  take  place,  and  the 
wound  may  heal  by  the  natural  process  before  described.     Suc- 
cess in  this  operation  depends  upon  selection  of  suitable  stock 
and  scion,  choice  of  the  proper  season,  freshness  of  the  cut  sur- 
faces, and,  generally,  exclusion  of  air  from  the  wound.     The 
methods  of  bringing  the  surfaces  of  the  stock  and  scion  together 
in  this  operation  of  grafting  are  innumerable,  but  for  the  pres- 
ent purpose  may  be  referred  to  two  principal  types :  (1)  that  in 
which  the  scion,  wholly  separated  from  the  plant  on  which  it 
grew  as  a  branch,  is  placed  in  some  sort  of  a  cleft  of  the  plant 
which  is  thenceforth  to  furnish  it  with  nourishment ;  (2)  that  in 
which  the  scion  is  still  retained  in  its  connection  with  the  parent 
plant,  but  is  bent  over  and  a  freshly  cut  surface  kept  in  contact 
with  a  cut  surface  of  another  plant,  until  the  scion  has  fairly 
become  attached  by  organic  union.     When  this  is  accomplished, 
it  is  cut  off  from  the  parent  plant.     This  type  of  grafting,  in  its 
many  varieties,  is  known  as  "  approach  grafting."    It  takes  place 
in  nature,  as  shown  in  the  following  paragraph. 

425.  Two  branches  of  one  plant  may  become  united  when, 
after  removal  of  a  section  of  bark  from  each,  the  two  denuded 
surfaces  are  kept  in  apposition  for  a  time.     Such  unions  of  axial 
organs  are  not  rare.     Occasionally  they  may  take  place  between 
two  shoots  at  a  point  near  the  root,  so  that  the  trunk  will  ulti- 
mately consist  of  a  single  deeply  grooved  stem.     The  union  may 
be  between  two  plants  of  the  same  species,  or  even  between 
plants  of  different  species.    The  attrition  of  two  branches  which 
have  grown  against  one  another  may  suffice  to  wear  off  the  bark 
on  both  down  to  the  cambium,  and  then,  if  their  exposed  surfaces 
are  held  together  for  a  while,  union  will  follow.     Such  natural 
grafts  are  met  with  frequently  at  the  borders  of  forests. 

426.  In  the  kindred  operation  of  budding,  a  bud  with  a  little 
of  the  tissue  behind  it  is  placed  in  a  cleft  in  the  bark  of  the 
stock,  so  that  the  cambium  layer  of  the  two  ma}7  come  into  close 
contact. 

427.  The  stem  may  be  invaded  by  parasitic  roots  at  any  part, 
and  its  subsequent  development  seriously  affected  thereby.    Such 
invasions  often  give  rise  to  swellings,  distortions,  etc.,  by  which 


RUDIMENTARY  AND  TRANSFORMED  BRANCHES.   153 

the  structure  of  the  stem  becomes  much  disguised.  In  the  case 
of  parasites  like  Phoradendron,  which  live  for  several  years,  a 
vertical  section  through  the  stem  of  the  host-plant  shows  how 
complete  the  union  is  between  the  host  and  parasite.  The  junc- 
tion has  been  well  compared  to  that  which  takes  place  between 
a  scion  and  its  stock,  since  the  newer-formed  tissues  of  both 
plants  become  perfectly  united,  and  their  subsequent  growth 
goes  on  together. 

428.  The  relations  of  the  root  to  the  stem  are  not  complicated, 
except  as  regards  the  bundles  at  the  "  crown"  of  the  root,  or  the 
point  where  it  meets  the  stem.     When  the  primary  structure  of 
dicotyledons  in  which  the  liber  of  the  root  is  arranged  in  one 
wajr  and  that  of  the  stem  in  another,  as  shown  in  Figs.  92  and 
112,  pages  111  and  137,  is  followed  by  the  formation  of  a  true 
cambium  ring,  the  subsequent  growth  of  root  and  stem  is  alike. 
Yearl}*  additions  are  made  in  the  root  in  the  same  way  as  in  the 
stem;  but  owing  to  the  unequal  resistance  exerted  by  the  soil, 
such  increments  are  often  very  irregular. 

Roots  may  be  produced  at  an}r  part  of  a  stem  where  adequate 
moisture  and  warmth  are  furnished ;  but  they  strike  off  chiefly 
at  nodes,  and,  in  the  case  of  cuttings,  also  at  the  seat  of  injury 
where  the  callus  is  formed.  Such  secondary  roots  form  on  stems 
in  much  the  same  manner  as  root- branches  do  upon  roots. 

429.  Rudimentary  and  transformed  branches  present  few  ana- 
tomical difficulties.     In  the  structure  of  a  branch  tendril,  or 
runner,  it  is  generally  easy  to  recognize  the  degree  of  reduction 
which  the  normal  fibre-vascular  system  has  undergone.     In  the 
case  of  underground  stems  and  branches  there  are  often  puzzling 
anomalies,  but  they  can  mostly  be  explained  by  the  following 
facts  brought  out  by  Costantin,1  who  has  made  a  special  study 
of  a  large  number  of  rhizomes:    1.  The  epidermis,  if  present, 
is  modified  by  becoming  cutinized  first  on  its  outer  walls,  where 
it  may  acquire  considerable  thickness,  and  later  on  its  lateral  and 
internal  walls.     2.  The  cortex  increases  either  by  enlargement 
of  its  cells  or  by  their  multiplication,  the  collenchyma  diminish- 
ing or  completely  disappearing.     3.  A  cork -layer  is  sometimes 
produced  at  an  early  period,  from  different  points  in  the  epi- 
dermis, in  the  cortical  parenchyma,  in  the  endodermis,  in  the 
peripheral  layer  of  the  bundles,  or,  lastly,  in  the  liber.     This 
replaces  to  a  great  extent  the  fibrous  layer  which  is  so  com- 
mon in  aerial,  but  never  much  developed  in  underground  stems. 

1  Ann.  des  Sc.  nat.,  ser  6,  tome  xvi.,  1883,  p.  164. 


154  MINUTE   STRUCTURE    OF   THE    STEM. 

4.  The  cortex  is  developed  largely  at  the  expense  of  the  pith. 

5.  There  is  only  slight  lignification  of  the  elements.    6.  There  is 
a  great  accumulation  of  reserve  materials. 

430.  The  relations  of  a  branch  to  the  main  axis  of  the  stem 
seldom  present  any  histological  difficulties,  the  tissues  of  the 
former   being   continuous  with   those  of  the  latter.     When   a 
branch  breaks  off  close  to  the  stem,  and  the  portion  remaining 
becomes  buried  by  stem-tissues  which  are  subsequently  produced, 
a  knot  is  formed. 

431.  Steins  of  vascular  cryptogams.1     The  following  outline 
indicates  the  principal  points  of  difference  between  the  stems  of 
Phaenogams  and  those  of  Ferns,  Equisetaceae,  and  their  allies. 

I.  In  vascular  cryptogams    the   fibro- vascular   bundles   are 
closed  and  as  a  rule  are  concentric.     1 .  In  Equisetum  they  are 
slender  and  are  arranged  in  a  circle.     From  the  median  line  of 
each  tooth  of  the  "  sheath"  (see  Gray's  Manual)  a  fascicle  de- 
scends perpendicularly  through  one  internode  and  divides  at  the 
one  below  into  two  branches,  which  unite  with  the  lateral  ones 
next  to  them.     2.  In  Osmundaceae  the  arrangement  of  the  con- 
stituent parts  of  the  central  cylinder  is  not  unlike  that  in  certain 
Coniferae.     3.  Lycopodiaceae  have  the  bundles  largely  dependent 
upon  the  arrangement  of  the  leaves,  but  the  axial  cylinder  is 
essentially  cauline.   4.  Ferns  proper  may  have  (a)  an  axial  cylin- 
der, or  (b)  several  concentrically  curved  bundles.    In  either  case 
there  may  also  be  isolated  and  rather  slender  bundles.     In  both 
cases  above  mentioned  the  bundles  coalesce  to  form  a  very  com- 
plicated network,  which  apparently  is  not  dependent  for  its  char- 
acter upon  the  distribution  of  the  leaves  upon  the  stem. 

II.  In  vascular  cryptogams  the  parenchyma  in  certain  places 
may  become  largely  sclerotic,  forming  dense  and  often  brown 
masses,  the  constituent  cells  of  which  are  sometimes  considerably 
elongated. 

III.  The  epidermis  in  Equisetaceae  is  strongly  silicified.     The 
stomata  in  these  plants  are  in  the  grooves  ;  their  development  is 
peculiar  in  that  from  one  epidermal  cell  four  guardian  cells  are 
formed  in  one  plane ;  but  soon  the  two  outer  cells  grow  more 
rapidly  and  crowd  down  the  two  inner  ones,  so  that  the  latter 
afterwards  become  distinctly  below  them.     The  epidermal  cells 
of  Ferns  frequently  contain  chlorophyll  granules. 

432.  Stems  of  mosses.     Here  no  true  fibro-vascular  bundles 
are  met  with,  but  elongated  cells  fill  their  place,  forming  what 

1  De  Bary  :  Vergleichende  Anatomie,  p.  289  et  seq. 


DEVELOPMENT   OF  THE   LEAF.  155 

has  been  termed  a  fascicle.  Comparison  of  these  threads — if 
such  they  can  indeed  be  called  —  with  the  rudimentary  fibro- 
vascular  bundles  of  some  water-plants  suggests  that  the  former 
are  bundles  of  the  simplest  possible  kind. 

The  parenchyma  cells  are  bounded  in  true  mosses  by  smaller, 
thicker-walled  cells,  which  do  not  contain  chlorophyll. 

THE   LEAF. 

433.  It  was  shown  in  322  that  roots  are  formed  under  the 
superficial  tissues  of  the  stem,  and  have  these  outer  layers,  or 
derivatives  from  them,  as  coverings  during  at  least  a  portion 
of  their  growth.     But  leaves  are  never  thus  covered  by  layers  of 
stem-tissue  ;    hence   they   are   termed   exogenous   productions, 
while  the  term  endogenous  is  applied  to  the  manner  in  which 
roots  are  formed. 

434.  Development.     In  the  earliest  stage  of  its  development 
the  leaf  is  a  mere  papilla  consisting  of  nascent  cortex  (periblem) 
and   nascent  epidermis  (dermatogeu).     As  soon  as  the  papilla 
elongates,  or  becomes  flattened,  some  of  its  interior  cells,  making 
up  procambium  tissue  (see  315),  differentiate  into  fibre-vascular 
bundles.     But  the  procambium  of  the  nascent  leaf  and  that  of 
the  cone  of  soft  tissue  constituting   the  growing-point  of  the 
stem  are  in  unbroken  connection  with  each  other ;  in  like  man- 
ner the  bundles  which  are  derived  therefrom  are  continuous,  and 
it  is  not  possible  to  detect  any  line  of  demarcation  between  them. 
In  fact,  the  newly  formed  bundles  in  a  young  leaf  appear  as  if 
they  are  merely  the  slender  prolongations  and  terminations  of 
those  in  the  young  stem.1 

435.  With  the  transverse  and  longitudinal  enlargement  of  the 
nascent  leaf  there  is  generally  more  or  less  curvature,  so  that 
the  outer,  lower,  and  earlier  leaves  infold  the  upper  leaves  and 
the  growing-point  of  the  cone.     In  most  cases,  some  of  the 
lower  leaves  which  thus  envelop  the  growing-point  become  modi- 
fied to  form  protecting  scales  ;  such  is  the  ordinary  structure  of 
buds  (see  "  Structural  Botany,"  page  42,  fig.  83). 


1  It  should  be  remembered,  however,  that  some  of  the  bundles  in  the  stem 
(see  365)  may  be  derived  from  procambium  peculiar  to  the  stem,  and  which 
does  not  extend  into  the  leaf.  Hence  it  is  necessary  to  distinguish  between 
stem-bundles,  common  bundles,  and  leaf-traces.  The  former  belong  to  the 
stem  alone ;  the  common  bundles  are  common  to  stem  and  leaf ;  the  leaf-traces 
are  leaf-bundles  which  are  in  the  stem  and  which  at  some  point  unite  with 
other  bundles  of  the  same  kind  to  form  common  bundles. 


156  MINUTE   STltUCTDBE  OF   THE  LEAF. 

436.  The  growth  of  the  young  leaf  is  plainly  terminal  at  first, 
—  that  is,  new  cells  are  added  just  in  front  of  the  older  ones;  but 
it  soon  becomes  intercalary  as  well,  new  cells  being  introduced 
between  those  previously  existing.  According  to  the  seat  of 
activity,  this  growth  may  be  basipetal  (the  zone  of  growth  being 
near  the  base  of  the  leaf-blade)  or  basifugal  (the  zone  nearer 
the  apex  of  the  leaf).  In  most  cases  the  base  of  the  leaf- blade 
and  the  stipules  early  attain  a  good  degree  of  development,  after 
which  the  petiole  appears. 

For  the  purpose  of  noting  the  peculiar  mode  in  which  the  leaf- 
blade  expands,  the  simple  device  suggested  by  Hales 1  is  perhaps 
as  good  as  any.  Through  a  piece  of  stiff  pasteboard  sharp  pins 
are  thrust,  and  fastened  at  equal  distances  from  each  other ;  for 
instance,  so  as  to  form  little  squares  of  \  inch  side.  B\-  this  sim- 
ple instrument  a  young  leaf  is  pierced  through  with  holes  at  equal 
distances ;  then  if  the  leaf  elon- 
gates more  than  it  widens  in  the 
space  thus  covered,  the  holes  will 
separate  in  the  direction  of  the 
length  of  the  leaf  more  than  in  that 
of  its  width.  The  injury  done  to 
the  leaf  by  these  small  perforations 
does  not  appear  to  check  or  other- 
wise much  modify  its  growth. 

437.  Fibro- vascular  bundles. 
The  distribution  of  fibro-vascular 
bundles  in  leaves  has  been  con- 
sidered in  Vol.  I.,  under  "Vena- 
tion." The  two  principal  types  of 
distribution  of  the  bundles,  there 
spoken  of  as  "veins  "  or  "nerves," 
were  shown  to  be  (1)  parallel, 
(2)  reticulated.  Parallel  venation 
(see  Fig.  119)  is  characterized  by 
having  large  "veins  "  or  "  nerves  " 
running  free  through  the  leaf  (that 
is,  not  connecting  with  each  other), 
or  without  any  obvious  anastomo- 
sis ;  while  in  reticulated  venation 
the  veins  form  a  more  or  less  com- 
plicated network. 

1  Statical  Essays,  vol.  i.,  1731,  p.  344. 
FIG.  119.    Venation  of  the  leaf  of  Convallaria  latifolia.    (Ettingshauaen. ) 


VENATION   OF   LEAVES. 


157 


438.  Parallel  venation  is  of  two 
principal  kinds  :  (1)  that  in  which 
large  nerves  run  in  long  curves 
from  the  base  to  the  apex  of  the 
leaf;  (2)  that  in  which  smaller 
nerves  run  generally  at  right  an- 
gles from  a  main  nerve  (or  midrib) 
to  the  edges  of  the  leaf.  In  both 
these  kinds  of  parallel  venation 
the  veins  are  more  or  less  con- 
nected by  means  of  inconspicuous 
cross-veinlets  and  by  the  anasto- 
mosing extremities,  but  some  of 
the  veins  may  be  free. 

439.  Reticulated  venation  is 
likewise  of  two  principal  kinds : 

(1)  palmate  (Fig.  120),  in  which 
relatively  large  veins  diverge  from 
each  other  at  the  base  of  the  leaf; 

(2)  pinnate  (Fig.  121),  in  which 


FIG.  120.    Venation  of  the  leaf  of  Aaarum  Europseum.    (Ettingshausen. ) 
FIG.  121.    Venation  of  the  leaf  of  Salix  grandifolia.    (Ettingshausen.) 


158  MINUTE   STRUCTURE   OF   THE   LEAF. 

side  veins  strike  off  through  the  whole  length  of  a  strong  midrib. 
In  both  these  cases  the  veins  divide  and  subdivide  and  have 
numerous  cross-connections  both  large  and  small,  until  the  ulti- 
mate ramifications  are  in  great  part  free. 

440.  Thus  it  appears  that  in  both  types  there  is  abundant 
communication  between  the  veins  of  leaves ;  but  in  some  cases, 
especially  in  rudimentary  and  submerged  leaves,  in  the  leaves  of 
Coniferae,  etc.,  the  veins  are  very  generally  free,  and  few  if  any 
cross-veinlets  are  met  with. 

441.  The  fibre- vascular  bundles  of  leaves  are  essentially  like 
those  of  stems  (see  365),  and  need  no  special  description  here. 
Their  extremities  are  for  the  most  part  trache'ids,  often  arranged 
in  double  rows,  but  their   diversities  of  structure  and  arrange- 
ment are  innumerable.    One  of  the  more  striking  special  cases  of 
these  has  been  already  shown  in  the  illustration  of  a  water-pore 
(v,  Fig.  55) ;  others  will  be  considered  later  (see  "Insectivorous 
Plants").     The  trache'ids  which  terminate  the  final  ramifications 
of  the  veins  in  leaves  are  in  close  contact  with  parenchyma  cells. 

442.  According  to  Casimir  De  Candolle,  the  leaf  ma}-  be  re- 
garded histologically  as  a  branch  with  its  upper,  that  is  its 
posterior,  side  atrophied.1 

443.  The  stipules  have  the  same  arrangement  of  elements  in 
their  fibro-vascular  bundles  as  the  blade,  —  that  is,  liber  below 
(outside),  wood  above  (inside).    But  in  ligules  (organs  which  are 
formed  by  radial  deduplication)   the   arrangement   is  just  the 
reverse  of  this,  —  the  liber  is  above,  the  wood  below. 

444.  Parenchyma.     The  forms  of  the  parenchyma  cells  which 
constitute  the  pulp  of  leaves  are :   (1)  spherical  or  nearly  so ; 
(2)  ellipsoidal,  sometimes  much  elongated  ;   (3)  branched,  some- 
times stellate.     Examples  of  these  three  are  often  met  with  in 
the  structure  of  a  single  leaf;  the  upper  layers  generally  being 
composed  of  ellipsoidal  cells,  the  lower  layers  of  more  nearly 
spherical  ones,  intermingled  with  some  which  are  branched. 

445.  The  arrangement  of  the  parenchyma  of  the  leaf-blade 
is  referred  by  de  Bary2  to  two  chief  types :    (1)  the  centric,  in 
which  the  chlorophyll  parenchyma  is  uniformly  disposed  through- 
out the  whole  organ ;   (2)  the  bifacial,  in  which  there  is  a  de- 
cided difference  between  the  compact  tissue  of  the  upper  and  the 
spongy  tissue  of  the  lower  side  of  the  leaf. 


'  Archives  des  sciences  de  la  Bibliotheque  universelle,  1868,  tome  xxxii. 
p.  32,  "un  rameau  a  face  posterieure  atrophied. " 
2  Vergleichende  Anatomic,  p.  423. 


PARENCHYMA    OF   THE   LEAF-BLADE. 


159 


446.  The  centric  arrangement  has  two  modifications  :  (1)  that 
in  which  the  whole  pulp  is  composed  of  chlorophyll  parenchyma, 
but  towards  its  mid- 
dle plane  has  larger 
cells  with  less  chlo- 
rophyll, and  some- 
times has  conspicu- 
ous lacunae  (many 
grasses,  Yucca  fila- 
mentosa,  Crassula, 
etc.)  ;  (2)  that  in 
which  it  is  composed 
of  layers  which  are 
uniformly  distrib- 
uted above  and  be- 
low a  middle  layer 
of  colorless  cells  free 

from  chlorophj-ll,  but,   in  succulents,  very  rich  in  sap  (Aloe, 

Mesembryanthemum, 
etc.).  In  both  the 
foregoing  modifica- 
tions the  upper  layer 
of  the  parenchyma 
ma}'  be  composed  of 
somewhat  longer  cells 
than  those  below,  and 
to  them  can  be  applied 
the  term  more  gener- 
ally given  to  those  in 
the  next  type,  namely, 
palisade-cells. 

447.  The  bifacial 
arrangement  has  the 
denser  tissue  in  that 
part  of  the  leaf  which 
is  exposed  to  the 
light.  This  usually  consists  of  several  layers  of  palisade  paren- 

PIG.  122.  Leaf  of  Pinus  Laricio.  Cross-section  of  a  part  of  the  leaf,  showing  the 
stomata,  hypoderma,  and  parenchyma.  The  folded  walls  of  the  parenchyma-cells  (see 
208)  are  plainly  shown  in  the  cells  below  the  resin-passage  (ffC),  where  they  have  been 
emptied  of  their  contents.  ( Kny. ) 

FIG.  123.  Transverse  section  of  a  leaf  of  Ilex  Aquifolium,  showing  arrangement  of 
the  parenchyma:  pp,  palisade  parenchyma;  pc,  spongy  parenchyma:  /i,  hypoderma; 
la,  fibro-vascular  bundle.  Stomata  are  found  only  upon  the  lower  surface  of  the  leaf. 
(Areschoug. ) 


160  MINUTE  STRUCTURE  OF   THE  LEAF. 

chyma ;  but  the  aggregate  thickness  of  these  may  not  be  so 
great  as  that  of  the  spongy  parenchyma  on  the  other  side  of 
the  leaf  (see  205). 

448.  In  some  plants  the  palisade  parenchyma  is  found  almost 
as  abundantly  in  the  under  as  in  the  upper  portions  of  the 
leaves.    Bessey *  has  shown  that  this  is  the  case  in  the  leaf  of  the 
Compass  plant  (Silphium  laciniatum)  :   "Its  chlorophyll-bearing 
parenchyma  is  almost  entirety  arranged  as  palisade  tissue,  so 
that  the  upper  and  lower  portions  are  almost  exactly  identical 
in  structure."    Another  plant  possessing  substantially  the  same 
leaf-structure  is  Lactuca  Scariola.    When  its  leaves  are  grown  in 
the  light,  they  take  a  vertical  position  (and  generally  stand  north 
and  south)  ;  but  if  grown  in  the  shade,  they  are  horizontal. 
The  leaves  which  are  developed  in  the  light  have  palisade  paren- 
chyma on  both  the  upper  and  under  portions  ; 2  but  those  which 
are  developed  in  the  shade  have  ordinary  parenchyma  above 
and  more  or  less  stellate  parenchyma  below. 

449.  According  to  Stahl,8  exposure  of  a  leaf  to  light  or  shade 
during  development  has  very  much  to  do  —  in  the  plants  thus 
far  examined  —  with  the  form  and  arrangement  of  its  paren- 
chyma.    The  leaves  of  the  common  beech  afford  good  material 
for  the  study  of  the  subject.     In  some  cases,  at  least,  those 
which  are  grown  in  the  deep  shade  of  a  grove  are  different  in 
texture  from  those  which  are  formed  in  bright  sunlight. 

450.  The  parenchyma  of  the  petiole  is  generally  much  like 
that  of  the  stem  to  which  it  is  attached  ;  layers  or  lines  of  thin- 
walled  collenchyma  sometimes  extending  without  interruption 
from  the  stem  into  the  petiole.     In  the  petioles  of  C3'cads  scle- 
rotic elements  like  those  of  the  stem  are  often  abundant,  and  are 
continuous  with  them.4 

451.  In  some  leaves  which  have  the  power  of  movement  the 
petiole  is  much  enlarged  at  its  base,  forming  what  is  known  as 
the  pulvinus.     The  parenchyma  of  this  structure  is  sometimes 
peculiar  in  being  thick-walled  on  the  upper  side  of  the  petiole 
and  thin-walled  on  the  under.     Other  peculiarities  will  be  de- 
scribed under  "  Movements." 

1  See  also  American  Naturalist,  1877. 

2  Pick  :  Botanisches  Centralblatt,  1882,  vol.  xi.  p.  441. 

8  Stahl  :  Ueber  den  Einfluss  des  sonnigen  oder  schattigen  Standortes  auf 
die  Ausbildung  der  Laubblatter,  Jena,  1883. 

Haberlandt,  on  the  other  hand,  does  not  think  the  effect  of  light  in  con- 
trolling the  character  of  leaf-structure  is  well  marked. 

*  Kraus :  Pringsheim's  Jahrb.,  1865,  vol.  iv.  p.  305. 


EPIDERMIS    OF   THE   LEAF. 


161 


452.  The  epidermis  of  the  leaf  is  continuous  with  that  of  the 
stem.    Its  principal  features  have  been  described  in  Chapter  II., 
and  only  the  following  need  now  be   recalled.     1.  It  may  be 
simple,  that  is,  composed  of  one  layer  of  cells  ;  or  multiple,  — 
of  more  than  one.      2.  Immediately  below  it  may  be  found  in 
some  cases  one  or  more  layers  of 

cells  known  as  the  hypoderma. 
3.  The  epidermal  cells  are  in  un- 
broken contact  with  each  other 
except  at  (1)  rifts,  (2)  water-pores, 
(3)  stomata.  4.  Their  surfaces 
may  exhibit  nearly  every  form  of 
trichome. 

453.  Glands   secreting    nectar 
are  found  on  different  portions  of 
the  leaves  of  various  plants ;  for 
example,   at  the  junction  of  the 
petiole  with  the  blade   (Poplar), 
at  the  base  of  the  petiole  (Cassia 
occidentalis),  on  the  lower  side  of 
the   midrib   of   the   leaf  (cotton- 
plant)  ,  or  scattered  over  the  lamina 
(turban  squash).    Such  glands  are 
particularly   noticeable    in   insec- 
tivorous plants,  as  Sarracenia  and 

Nepenthes  (see  Part  II.).  On  making  a  section  of  one  of  the 
nectar-glands  found  on  a  young  poplar  leaf,  the  epidermis  will 
be  seen  to  be  transformed  into  a  double  layer  of  thin-walled, 
elongated  cells  forming  the  secreting  surface,  which  is  charged, 
together  with  the  parenchyma  lying  below  it,  with  a  syrup  de- 
rived from  the  transformation  of  starch.  At  times  the  secretion 
from  a  gland  is  so  abundant  that  drops  of  considerable  size 
collect  upon  the  surface  of  the  leaf,  and  if  rapid  evaporation 
takes  place,  crystals  of  sugar  are  deposited  at  the  gland.1 

454.  The  leaves  of  submerged  phaenogams,  for  example  those 
of  Potamogeton  and  Myriophyllum,  possess  no  true  epidermis; 
the  parenchyma  is  therefore  in  direct  contact  with  the  surround- 


1  Trelease  :  Nectar  and  its  Uses,  in  Report  on  Cotton  Insects  (United  States 
Department  of  Agriculture,  1879),  and  Nectar-Glands  of  Populus,  Botanical 
Gazette,  vol.  vi.  p.  284. 

FIG.  124.  Transverse  section  through  leaf  of  Camellia  (Thea)  viridis,  showing :  a 
epidermis ;  6,  branched  liber-cell ;  d,  oil-drop ;  e,  crystals     (Mirbel.) 
11 


162  MINUTE   STRUCTURE   OP    THE   LEAP. 

ing  water.  On  the  external  surface  its  thin-walled  cells  are  in 
close  contact  (there  being  nothing  answering  to  stomata)  ;  but 
in  the  interior  of  the  leaf  there  are  often  lacunae  filled  with  air. 
These  were  thought  by  Brongniart  to  be  essentially  the  same  as 
those  cavities  found  in  the  parenchyma  of  many  marsh  plants. 

The  veins  of  submerged  leaves  have  no  true  ducts  ;  the  elon- 
gated fascicles  generally  consisting  merely  of  rows  of  elongated 
cells.1 

455.  Roots  ma}'  be  produced  from  leaves  in  much  the  same 
way  as  they  are  from  stems ;  that  is,  some  of  the  cells  at  the 
liber  may  divide  in  such  a  manner  as  to  form  a  protuberance 
which  pushes  before  it  a  part  of  the  endodermis.     As  the  root 
thus  formed  emerges,  the  tissues  are  speedily  produced,  the  wood 
being  continuous  with  the  wood  of  the  leaf,  the  liber  with  its 
liber.     Roots  ma}r  arise  naturally  in  some  leaves  by  simply  plac- 
ing them  in  contact  with  moist  earth,  or  they  may  be  produced 
artificially  by  mutilation  of  the  petiole  or  lamina.     Bryophyllum 
cal3'cinum  affords   a   good   example   of  the   former ;   Begonia, 
Peperomia,  etc.,  of  the  latter  mode  of  origin. 

456.  Buds  may  form  spontaneously  on  the  margin  of  leaves, 
especially  those  in  contact  with  a  moist  surface,  or  they  may 
grow  from  the  cells  under  the  scar  where  a  mutilated  leaf  has 
healed. 

457.  In  some  of  these  cases  only  the  epidermal   cells  take 
part  in  producing  the  meristem  from  which  the  bud  is  developed  ; 
in  others  the  parenchyma  just  below  the  epidermis  also  divides, 
or  the  cells  under  the  scar  may  produce  all  the  axial  tissue  ele- 
ments.  Begonia  is  an  example  of  the  first  method  of  production, 
Bryophyllum  of  the  second,  Peperomia  of  the  third. 

It  is  interesting  to  observe  that  in  all  these  cases  the  bud  forms 
without  the  intervention  of  the  fibro-vascular  bundles  of  the  leaf. 
The  newly  formed  axis  has  fibro-vascular  bundles,  which  may 
anastomose  with  those  pre-existent  in  the  leaf,  but  usually  they 
are  entirely  distinct.  The  axis  is,  however,  provided  with  its 
own  root-system,  and  after  a  time  it  becomes  severed  by  a  plane 
of  cork  from  the  leaf  which  produced  it. 

458.  Fall  of  the  leaf.     In  deciduous  plants  the  leaf  separates 
from  the  stem  or  twig  by  the  formation  of  a  plane  of  cells'1 
cutting  sharply  through  the  petiole  at  or  very  near  its  base. 
The  dividing  plane  may  be  partially  formed  early  in  the  growing 

1  Brongniart  :  Ann.  des  Sc.  nat.,  tome  xxi.,  1830,  p.  442. 

3  Called  by  Mohl  the  separative  layer  (Botanische  Zeitung,  1860,  p.  1). 


FALL   OF    THE    LEAF.  163 

season,  but  generally  it  is  not  far  advanced  in  development  until 
near  the  end  of  summer.  The  leaflets  of  the  larger  compound 
leaves  —  for  instance,  those  of  Ailanthus,  Gymnocladus,  Ju- 
glans,  etc.  —  afford  excellent  material  for  examining  the  process 
of  defoliation.  Strong  leaves  of  any  of  the  plants  mentioned 
are  to  be  kept  between  damp  (not  wet)  paper  in  a  warm  place 
for  a  number  of  hours,  when  the  formation  of  the  dividing  plane 
can  be  observed.  The  plane  is  so  far  completed  by  the  end  of 
the  second  or  third  day  that  the  leaflets  fall  with  the  slightest 
touch. 

459.  The  strong  leaves  of  horse-chestnut  are  employed  by 
Strasburger  as  material  for  demonstrating  the  process  of  defolia- 
tion.    He  says  that  alcoholic  material  answers  very  well  for  the 
purpose,  but  that  it  happens  occasionally  that  the  distinctive 
brown  color  of  the  cells  adjoining  the  cutting  plane  is  nearly  or 
quite  lost.     The  petiole  is  to  be  cut  through  in  its  median  line, 
and  then  several  very  thin  longitudinal  sections  parallel  to  this 
are  to  be  carefully  made  and  placed  at  once  in  water.    In  a  good 
preparation  the  cells  making  up  the  cutting  plane  should  be 
clearl}'  seen  extending  from  the  epidermis  of  the  petiole  to  the 
fibro-vascular  bundles.     If  the  leaf  was  taken  at  just  the  right 
time,  the  preparation  should  show  also  that  the  cutting  plane 
has  invaded  even  the  tissue  of  the  fibro-vascular  bundles.     The 
plane  consists  of  one  to  several  layers  of  cells,  some  of  which 
are  plainly  cutinized  ;  thus,  as  a  rule,  the  place  of  separation  is  a 
scar  healed  before  the  leaf  falls. 

It  happens  frequently  that  changes  take  place  at  the  middle 
portion  of  the  cutting  plane,  by  which  its  layers  near  the  leaf 
are  forcibly  separated  from  those  nearer  the  stem  ;  in  such  cases 
the  leaf  falls  because  it  is  forced  off.1 

460.  The  excision  of  the  leaf  usually  takes  place  at  the  base 
of  the  petiole,  so  that  the  surface  of  the  scar  is  even  with  the 

1  "The  provision  for  the  separation  being  once  complete,  it  requires  little 
to  effect  it ;  a  desiccation  of  one  side  of  the  leaf-stalk,  by  causing  an  effort  of 
torsion,  will  readily  break  through  the  small  remains  of  the  fibro-vascular  bun- 
dles ;  or  the  increased  size  of  the  coming  leaf-bud  will  snap  them  ;  or,  if  these 
causes  are  not  in  operation,  a  gust  of  wind,  a  heavy  shower,  or  even  the 
simple  weight  of  the  lamina,  will  be  enough  to  disrupt  the  small  connections 
and  send  the  suicidal  member  to  its  grave.  Such  is  the  history  of  the  fall  of 
the  leaf.  We  have  found  that  it  is  not  an  accidental  occurrence,  arising  simply 
from  the  vicissitudes  of  temperature  and  the  like,  but  a  regular  and  vital  pro- 
cess, which  commences  with  the  first  formation  of  the  organ,  and  is  completed 
only  when  that  is  no  longer  useful"  (Dr.  Inman,  in  Henfrey's  Botanical 
Gazette,  vol.  i.  p.  61). 


164  MINUTE   STRUCTURE  OF  THE  LEAP. 

surface  of  the  stem  ;  but  it  may  occur  a  little  higher  up,  so  that 
some  of  the  petiole  remains  attached  to  the  stem 1  (Rubus, 
Oxalis,  etc.). 

461.  Evergreen  leaves  are  those  which  remain  upon  the  stem 
without  much  apparent  change  during  at  least  one  period  of 
suspension  of  vegetation.     The  leaves  of  some  evergreens  per- 
sist through  only  one  year,  falling  off  as  soon  as  those  of  the 
succeeding  year  have  fully  expanded.    It  is  not  unusual  in  warm 
temperate  climates  to  have  trees  and  shrubs  which  are  normally 
deciduous  in  colder  regions  retain  their  leaves  until  new  ones 
are  produced. 

Pines  and  spruces  lose  some  of  their  oldest  leaves  every  j'ear, 
but  new  ones  are  as  regularly  formed.  Their  branches  are  never 
completely  defoliated,  but  may  bear  at  one  time  the  leaves  which 
have  been  formed  during  several  years. 

462.  The  colors  assumed  by  leaves  before  they  fall  can  be 
better  examined  after  the  subject  of  the  pigment  of  chlorophyll- 
granules  has  been  treated  in  Part  II. 

463.  The  fronds  of  ferns  and  the  leaves  of  their  allies  present 
few  peculiarities,  and  do  not  need  to  be  here  examined.     The 
formation  in  ferns  of  the  sori,  or  spore-dots,  the  sporangia,  or 
spore-cases,  and  the  spores  themselves  falls  properly  within  the 
province  of  Volume  III. 

464.  The  leaves  of  mosses  are  characterized  by  great  sim- 
plicity of  structure.     For  their  study  any  of  the  species  of  Poly- 
trichum,  or  Hair-cap  Moss,  will  answer.     In  these  there  is  no 
true  fibro-vascular  bundle ;  a  series  of  somewhat  elongated  and 
rather  firm  cells,  known  as  the  conducting  thread,  takes  its  place. 
Upon  this  conducting  thread  the  parenchyma  cells  are  distributed 
more  or  less  regularly,  on  one  side  forming  slender  elevations 
four  or  five  cells  in  height.     The  cells  contain  chlorophyll,  and 
generally  much  starch.2 

465.  In  the  thallophytes  there  is  no  clear  distinction  of  leaf 
and  axis  ;  the  tissue  consists  throughout  of  parenchyma  more  or 
less  modified.     In  some  algae  there  is  often  a  lateral  parting  of 
the  frond  into  segments  resembling  leaves ;  but  as  they  are  not 
leaves  morphologically,  they  need  no  further  consideration  here. 

1  For  full  and  interesting  accounts  of  the  changes  which  cause  the  fall  of 
the  leaf,  see  Mohl's  paper  in  Botan.  Zeitung,  1860,  p.  1,  and  also  Van  Tieghem 
and  Guignard  in  Bull.  Soc.  hot.  de  France,  1882. 

2  In  Strasburger's  Botanische  Practicura,  p.  304,  the  student  will  find  a 
full  and  interesting  account  of  the  structure  of  the  leaves  of  Polytrichum  and 
Mniuiu. 


WORKS  OF  REFERENCE.  165 

In  the  examination  of  the  tissues  of  the  organs  of  vegetation 
the  student  is  referred  to  the  following  works  :  — 

DE  BARY.  Vergleichende  Anatomic  (Leipzig,  1877).  An  octavo  volume 
of  about  660  pages,  of  which  an  excellent  English  translation  is  newly  pub- 
lished under  the  title,  "  Comparative  Anatomy  of  the  Vegetative  Organs  of 
Phanerogams  and  Ferns,"  by  A.  De  Bary.  Translated  by  F.  0.  Bower  and 
D.  H.  Scott,  1884.  This  exhaustive  treatise  gives  all  needful  references  to 
the  literature  of  the  subject  up  to  1876. 

Mom,.  Vermischte  Schriften.  This  is  a  collection  of  Hugo  von  Mold's 
most  important  works,  which  have  appeared  from  time  to  time  in  various 
journals. 

STRASBURGER.  Das  botanische  Practicum  (Jena,  1884).  This  work,  of 
which  an  English  translation  is  promised,  is  of  very  great  use  both  to  beginners 
and  advanced  students  of  Histology.  The  directions  for  procuring,  preserving, 
and  using  material  are  explicit,  and  for  the  most  part  are  conveniently  ar- 
ranged. The  volume,  of  more  than  600  pages,  is  divided  into  separate  studies, 
such  as  the  structure  of  the  bast  and  wood  of  the  pine,  the  anatomy  of  a  few 
common  leaves,  etc. 

OLIVER.  Bibliography  of  the  Stems  of  Dicotyledons  (Natural  History  Re- 
view, 1862  and  1863).  A  citation  of  the  more  important  works  on  the  stems 
of  different  dicotyledons,  arranged  according  to  the  natural  families. 

For  a  treatment  of  the  anatomy  of  the  organs  of  aquatics  and  parasites,  the 
fully  illustrated  work  of  Chatin  may  be  consulted. 

Those  curious  to  examine  the  diverse  and  now  mostly  abandoned  views 
regarding  the  growth  and  structure  of  the  stem,  will  find  much  of  interest  in 
the  works  of  Du  Petit  Thouars  and  of  Gaudichaud.  An  account  of  these  and 
other  views  will  be  found  in  Schleiden's  "  Principles  of  Botany  "  (1849). 


CHAPTEE  IV. 

MINUTE    STRUCTURE    AND    DEVELOPMENT    OF    THE 
FLOWER,   FRUIT,   AND   SEED. 

THE   FLOWER. 

466.  IN  Volume  I.  Chapter  VI.,  it  has  been  shown  that  a 
flower  is  to  be  regarded  as  a  modified  branch  with  very  short 
internodes  and  with  the  foliar  expansions  assuming  forms  unlike 
those  of  ordinary  leaves.     In  the  outer  circle  —  the  calyx  —  the 
parts  have  frequently  the  texture  and  color  of  foliage  ;  but  in  all 
the  other  circles  of  the  flower  the}7  are  notably  metamorphosed. 
Notwithstanding  their  disguises,  the  parts  of  the  flower  are  iden- 
tifiable as  leafy  structures  arranged  upon  an  axis.     On  the  care- 
ful examination  of  flower-buds  the  homology  between  all  their 
parts  and  those  of  a  leaf-bud  becomes  evident.     In  fact,  in  their 
earliest  state  it  is  impossible  to  discriminate  between  these  two 
kinds  of  buds.      Each  has  a  rounded  or  cone-like  extremity, 
upon  which  are  disposed  at  definite  points  the  papillae  which  are 
to  develop  into  foliar  organs.      In  one,  these  papillae  become 
green  leaves ;   in  the  other,  the  parts  of  a  flower. 

467.  Two  features    in   the  development    of  flowers   require 
special  attention  ;  namely,  the  sequence  in  which  the  organs  are 
produced,  and  the  order  in  which  the  histological  elements  make 
their  appearance.     But  it  is  not  well  in  any  given  case  to  under- 
take the  examination  of  the  development  either  of  the  organs  or 
of  the  tissues  which  compose  them,  until  the  student  has  made 
himself  familiar  with  the  characters  of  the  full-grown  flower. 

468.  Undeveloped  racemes  afford  the  best  material  for  the 
study  of  the  developing  organs  of  the  flower,  and  it  is  generally 
possible  to  find  in  a  single  young  cluster  flowers  in  all  the  earlier 
stages  of  development.     There  are  two  good  methods  of  pre- 
paring the  material  for  the  compound  microscope  :  (1)  the  whole 
raceme,  first  decolorized  by  absolute  alcohol  and  then  softened 
by  glycerin,  is  to  be  dissected  under  a  simple  lens,  and  the  sepa- 
rate flowers  are  to  be  bleached  with  sodic  hypochlorite ;  or  (2)  the 


DEVELOPMENT   OP   THE   FLOWER. 


167 


very  tip  of  the  raceme  is  to  be  cut  squarely  across  and  placed 
with  a  drop  of  water  under  a  cover-glass,  when  some  of  the  young- 
est flowers  can  be  seen  either  standing  vertically  or  slightly  in- 
clined. The  air  can  be  drawn 
out  from  the  specimen  by 
placing  the  slide  for  a  min- 
ute under  the  air-pump  ;  the 
outlines  of  the  floral  organs 
will  then  be  distinct. 

469.  A  still  better  method 
is  to  make  tolerably  thick 
vertical  sections  of  separate 
flowers,  one  of  which  in 
each  flower  must  be  through 
the  median  line  ;  and  then,  125 

arranging  the  sections l   in 

their  proper  sequence,  clear  them  for  examination  either  by  the 
use  of  potassic  hydrate  (as  directed  in  24),  or  b}-  the  following 
method,  recommended  by  Stras- 
burger  as  applicable  to  many  cases 
of  thick  masses  of  soft  tissues : 
Treat  the  part  first  with  absolute 
alcohol  for  a  day  or  two,  and  then 
place  it  in  concentrated  carbolic 
acid,  after  which  it  becomes  clear. 
For  the  carbolic  acid  either  of  the 
126  following  may  be  substituted, — 

(1)  three  parts  of  oil  of  turpen- 
tine and  one  part  of  creosote,  or  (2)  equal  parts  of  alcohol  and 
creosote. 

By  any  one  of  these  methods  it  is  generally  possible  to  obtain 
preparations  of  sufficient  clearness  to  exhibit  in  optical  section 
all  the  internal  tissues. 


1  Pfeffer  advises  that  the  young  flowers  should  first  be  tinged  with  anilin 
blue,  and  then  imbedded  in  a  strong  solution  of  gum-arabic  (to  which  a  little 
glycerin  has  been  added  to  prevent  brittleness  of  the  mass  on  drying).  Then, 
when  the  gum  is  dry,  sections  can  be  easily  cut  in  any  direction. 

FIG.  125.  Lysimachia  quadrifolia.  Flower  seen  from  the  side,  and  somewhat  ob- 
liquely, the  calyx  being  removed.  At  this  period  the  parts  of  the  corolla  have  not 
coalesced :  sp,  place  where  the  excised  sepals  were;  p,  petal;  st,  stamen.  (Pfeffer.) 

FIG.  126.  Lysimachia  quadrifolia.  Thin  longitudinal  section  through  the  median 
line  of  a  flower,  in  which  the  organs  are  beginning  to  form.  Before  the  sinuses  of  the 
calyx,  as  well  as  before  its  lobes,  cell-division  has  taken  place  on  all  sides;  for  instance, 
at  st,  n,  and  x.  (Pfeffer.) 


168 


MINUTE   STRUCTURE  OF  THE  FLOWER. 


470.  The  fully  grown  flower  of  Lysimachia  quadrifolia  is  thus 
characterized :  Calyx  hypogynous,  deeply  5-parted,  the  lobes 
valvate  or  veiy  slightly  imbricated  in  the  bud  ;  corolla  hypogy- 
nous, wheel-shaped,  and  deeply  5-parted  with  hardly  any  tube, 
its  lobes  convolute  in  the  bud  ;  no  teeth  between  the  lobes  of  the 
corolla ;  lobes  of  the  corolla  longer  than  the  narrow  lanceolate 
lobes  of  the  calyx ;  stamens  of  unequal  length,  plainty  united  at 
the  base,  inserted  opposite  the  lobes  of  the  corolla,  glandular ; 
anthers  barely  oblong ;  ovary  one-celled,  surmounted  by  an  un- 
divided style  and  stigma,  and  containing  10-15  ovules  on  a 
central  placenta. 


Fig.  126  shows  the  appearance  of  a  very  young  flower  of  this 

species  ;  on  the  rounded 
or  somewhat  flattened 
apex  of  the  axis  minute 
elevations  are  seen,  the 
outer  being  the  nascent 
sepals.  Fig.  127  shows 
the  flower  in  a  more  ad- 
vanced stage.  Fig.  128 
represents  a  portion  only, 
the  right,  in  a  still  more 
advanced  condition. 
Fig.  129  exhibits  all  the 
organs  of  the  flower,  so 
far  as  they  can  be  shown 

FIG.  127.  Lysimachia  quadrifolia.  A  longitudinal  section  through  a  flower  some- 
what more  advanced  than  in  Fig.  126;  the  letters  are  the  same  as  in  Fig.  128.  (Pfeffer.) 

FIG.  128.  Lysimachia  quadrifolia.  Longitudinal  section  through  an  elevation  which 
is  considerably  advanced  before  the  appearance  of  the  petals:  st,  stamen;  n,  cells 
where  the  petals  will  appear.  (Pfeffer.) 

FIG.  129.  Lysimachia  quadrifolia.  A  longitudinal  section  through  a  flower  in  which 
all  the  organs  are  well  developed,  and  even  the  parts  of  the  ring  by  which  the  corolla- 
lobes  are  to  coalesce  have  begun  to  grow :  sp,  sepal ;  p,  petal,  or  corolla-lobe ;  at,  stamen ; 
g,  ovary ;  c,  placenta ;  sp.  u,  and  p.  u,  the  tissue  uniting  the  parts  of  the  calyx  and  corolla 
respectively.  (Pfeffer.) 


OBDER  OF  APPEARANCE  OF  FLORAL  ORGANS.      169 

in  a  single  longitudinal  section.  Comparison  of  these  figures 
gives  a  clear  idea  of  the  sequence  in  which  the  organs  make 
their  appearance ;  namely,  in  acropetal  succession,  —  that  is, 
the  3'ounger  or  newer  are  always  nearest  the  extremity. 

471.  According  to  Payer,  the  sepals  always  precede  the  petals, 
the  petals  the  stamens,  and  the  stamens  the  pistils,  in  time  of 
appearance.  But  in  a  few  cases,  of  which  Lysimachia  is  one, 
it  may  happen  that  a  given  circle  of  organs  is  somewhat  de- 
Ia3'ed  in  forming;  for  instance,  in  the  figures  the  stamens  are 
seen  as  considerable  protuberances  before  the  petals  are  clearly 
outlined.  This  fact  has  been  considered  by  some  to  indicate 
that  the  corolla  in  such  cases  consists  of  an  intercalated  whorl 
between  two  other  whorls  already  somewhat  developed.  But  a 
careful  examination  of  Lysimachia  and  most  other  cases  shows 


rather  that  the  petals  or  the  corolla-lobes  are  laid  down  in  their 
proper  sequence,  but  that  they  are  temporarily  outstripped  by 
the  sepals  and  the  stamens. 

The  appearance  of  the  forming  flower  when  seen  in  vertical 
section  is  shown  in  Fig.  130,  and  a  perspective  view  is  given 
in  Fig.  125,  exhibiting  the  late-appearing  petals  and  the  much 
larger  stamens. 

472.  Since  the  several  organs  of  the  flower  are  modified 
leaves  symmetrically  arranged  on  an  axis,  the  histological  con- 
stituents of  a  leafy  branch  will  be  found  in  the  flower,  albeit 
much  modified  in  some  of  their  characters.  These  constituents 
are,  (1)  a  framework  of  fibro-vascular  tissue,  upon  which  is 
extended  (2)  parenchyma,  covered  by  (3)  epidermis. 

FIG.  130.  Lysimachia  quadrifolia.  Longitudinal  section  through  a  flower  in  which 
the  corolla  is  just  appearing.  The  elevation  on  the  right  has  been  cut  through  exactly 
in  the  median  line,  while  that  on  the  left  has  been  cut  on  its  edge.  Letters  the  same  as 
in  Fig.  129.  (Pfeffer.) 


170  MINUTE    STRUCTURE   OF   THE   FLOWER. 

473.  The  flbro-vascular  bundles  of  the  flower  are  essentially 
the  same  as   the   collateral   bundles   found   in   ordinary  green 
leaves,  except  that  their  elements  are  usually  more  delicate  in 
texture,  and  in  the  inner  whorls  of  organs  very  much  reduced. 

474.  The  parenchyma  calls  for  no  special  remark  beyond  allu- 
sion to  the  fact  that  some  one  of  the  different  kinds  of  internal 
glands  is  frequently  associated  with  it. 

475.  The  epidermis  has  stomata,  —  which  are  generally  rudi- 
mentary, — -  and  most  of  the  forms  of  trichomes.    One  of  the  most 
interesting  peculiarities  of  structure  presented  by  the  parts  of 
the  flower  is  found  in  the  papillar  outgrowths  alluded  to  in  222. 
These  are  of  course  minute  and  short  hairs,  which,  owing  to 
their  abundance,  impart  a  velvety  appearance  to  the  part  on 
which  they  occur.     This  appearance  is  well  shown  by  the  petals 
of  a  very  large  number  of  the  flowers  most  common  in  cultiva- 
tion. 

476.  The  cuticle  of  the  epidermal  cells  of  the  more  delicate 
petals  is  sometimes  very  distinctly  striated  in  an  irregular  man- 
ner.    The  walls  of  the  cells  generally  have  a  sinuous  outline. 

477.  The  colors   of  petals   and  other  colored  parts  of  the 
flower   are   dependent   either    on    the   presence    of    corpuscles 
(the  colored  plastids)  or  of  matters  dissolved  in  the  cell-sap. 
The  following  account  of  the  coloring-matters  in  the  very  com- 
mon Viola  tricolor  is  condensed  from  Strasburger. 

A  vertical  section  through  a  petal  exhibits  the  epidermis  of  the 
upper  side  as  consisting  of  elongated  papillae,  while  that  of  the 
lower  side  has  only  slightly  rounded  ones.  Just  below  the  epi- 
dermis of  the  upper  side  there  is  a  layer  of  compact  cells,  under 
which  are  several  rows  of  smaller  cells  with  conspicuous  inter- 
cellular spaces.  The  cells  of  the  epidermis  of  both  sides  contain 
violet  sap  and  yellow  granules  ;  the  layer  of  compact  cells  under 
the  epidermis  of  the  upper  side  contains  only  yellow  granules. 
The  striking  diversities  in  color  presented  by  different  parts  of  a 
given  petal  depend  wholly  upon  combinations  of  these  two  ele- 
ments of  color ;  namely,  violet  sap  and  yellow  granules.  In 
some  places  which  are  devoid  of  either  of  these  elements  there 
are  white  spots ;  at  these  places  the  light  is  refracted  and  re- 
flected by  the  intercellular  spaces  which  contain  air.  If  the  air 
is  removed  by  pressure,  the  spots  will  become  transparent. 

478.  The  cell-sap  in  the  parts  of  the  flower  may  have  almost 
any  color,  especially  shades  of  red  and  blue ;  from  this  sap  the 
coloring-matter  sometimes  crystallizes  in  the  form  of  short  and 
slender  needles  ;  for  instance,  in  Delphinium  Consolida. 


DEVELOPMENT   OF    STAMENS. 


171 


479.  Development  of  the  stamens.     The  following  outline  may 
serve  as  an  introduction  to  the  stud}-  of 

the  development  of  the  stamens.  At 
first,  the  stamen  exists  as  a  mass  of 
homogeneous  parenchyma  ;  later,  a  del- 
icate fascicle,  continuous  with  one  in  the 
filament,  becomes  differentiated  in  one 
part  of  the  stamen,  the  connective.  Four 
longitudinal  ridges  appear  on  the  an- 
ther, which  coincide  with  four  lines  of 
large  cells  within.  These  cells  give  rise 
to  the  mother-cells  of  the  pollen  and  to 
the  very  delicate  pollen-sac.1 

480.  The  mother-cells  of  the  pollen 
have  at  first  thin  walls,  but  later  these 
become    irregularly    thickened.      In   a 
large  number  of  cases  —  many  mono- 
cotyledons, and  most  if  not  all  dicoty- 
ledons —  the  nucleus  of  a  mother-cell  divides  into  two  nuclei, 

which   themselves  divide 
D  at    right    angles    to    the 

plane  of  the  first  division, 
thus  producing  four  nuclei 
forming  a  tetrahedron. 
Cell-walls  are  next  formed, 
and  four  cells  are  pro- 
duced, which  are  called 
the  tetrad.  After  the 
mother-cells  of  the  pollen 
have  been  changed  into 
tetrads,  the  mass  of  pro- 
toplasm in  each  of  the 
cells  of  a  tetrad  becomes 
covered,  as  Strasburger 
has  shown,  with  a  new 

1  The  cells  which  make  up  the  layer  forming  the  pollen-sac  are  known, 
collectively,  as  the  Archcsporium.  The  epithelium  which  lines  the  pollen-sac 
has  been  termed  the  Tapctum. 

FIG.  131.  Orchis  maculata.  A  pollen-mass  in  process  of  enlargement,  with  the  anther- 
wall  on  the  outside:  ep,  epidermis;  1,  layer  of  cells  under  the  epidermis  remaining  un- 
divided ;  2'  and  3',  layers  arising  from  division  ;  3',  the  endnthcriiim.  The  little  mass 
cm,  formed  by  the  mother-cells,  is  surrounded  by  a  thickened  wall.  3f°.  (Gnignard  ) 

FIG.  132.  A,  transverse  section  of  a  young  anther  of  Mentha  aquatica  ;  B,  a  fourth 
of  this  magnified;  C,  section  through  a  young  anther  of  Symphytum  orientale;  D,  a. 
fourth  of  this  magnified  The  dotted  lines  in  A  and  C  show  the  part  taken  for  exami- 
nation. E,  section  of  a  youiig  anther  of  I^eucanthemum  vulgare.  (Warming.) 


172  MINUTE  STRUCTURE  OF  THE  FLOWER. 

cell-wall,  the  proper  cell-wall  of  the  pollen-grains.  This  wall 
may  be  variously  marked,  sculptured,  and  cuticularized,  giving 
rise  to  the  characteristic  forms  and  features  of  the  grains  as 
they  are  met  with  in  the  mature  flower.  In  gymnosperms,  the 
development  of  pollen-grains  differs  from  that  described  in  some 
particulars  which  are  interesting  chiefly  from  their  resemblance 
to  what  occurs  in  the  higher  cryptogams. 

481.  The  stigma  is  a  surface  formed  of  peculiar  cells  which 
secrete  a  viscid,  saccharine  matter,  slightl}*  acid  in  reaction.     In 
some  cases  the  walls  of  the  stigmatic  cells  undergo  the  mucilagi- 
nous modification  (Solanum,  etc.).     The  wide  differences  which 
exist  in  the  character  of  the  cells  of  the  stigma  are  illustrated  by 
the  following  examples:  (1)  cells  with  no  marked  papilla?,  as  in 
Urabelliferae ;   (2)  papillose,  as  in  Salvia,  Convolvulus,  Spiraea ; 
(3)  hairy,  as  in  Hypericum,  Geranium  ;  (4)  with  compound  hairs, 
as  in  Reseda.     In  some  of  the  above  the  cells  are  rather  loosely 
aggregated,  while  in  others  they  are  much  more  compactly  com- 
bined.    Below  the  stigma  the  style  often  has  collecting  hairs,  as 
in  Composite,  Carapanulaceae,  etc.  (see  Volume  I.  page  222). 

482.  The  style  is  a  prolongation  of  the  ovary,  and  shares  with 
it  its  fascicular  system.     In  the  interior  there  is  a  slender  thread 
of  loose  tissue  made  up  of  thin-walled  cells  containing  consider- 
able food-material,  starch  or  oil,  etc.     The  cell-walls  often  pass 
into  the  mucilaginous  condition.    The  style  is  sometimes  tubular, 
and  lined  with  the  tissue  just  described. 

483.  The  simple  ovar}'  is  a  modified  leaf-blade  provided  with 
epidermis,  parenchyma,  and  a  fascicular  system.    The  epidermis 
of  the  outside  of  the  ovary,  and  that  which  lines  its  cavity,  may 
have  all  the  characters  of  ordinary  epidermis  ;  stomata  and  hairs 
ma}-  be  present,  the  latter  often  being  mere  papillae,  which  upon 
the  ripening  of  the  ovary  into  the  fruit  become  long  hairs. 

484.  In  the  interior  of  the  ovary  there  is  frequently  a  pecul- 
iar modification,  either  of  the  epidermis  itself  or  of  the  sub- 
jacent parenchyma  as  well.      In  such  cases  very  loose  tissue, 
sometimes  appearing  as  if  composed  of  felted  hairs,  lines  the 
cavity  of  the  ovary  (or  is  found  at  some  one  portion  of  it).    The 
walls  of  this  tissue  ma}*  undergo  the  mucilaginous  modification 
either  in  whole  or  in  part.      Its  cells  contain   a  considerable 
amount  of  food-materials  (oil  and  starch).     This  loose  tissue, 
together  with  that  of  the  same  character  found  in  the  style,  is 
known  as  conductive  tissue,  and  serves  as  a  path  of  least  resist- 
ance for  the  penetrating  pollen-tube  (see  Part  II.). 

48o.    The  distribution  of  the  fibro-vascular  bundles  in  ovaries 


BlBEO-VASCtTLAR  BUNDLES  OF  THE  OVARY.        173 


is  of  much  interest,  and  can  best  be  examined  under  the  two 
heads  of  "  Simple  Pistils"  and  "  Compound  Pistils." 

486.  Simple  Pistils.     The   fibro-vascular  bundle   consists   of 
wood  and  liber  running  through  the  median  line  of  the  carpellary 
leaf,  —  that  is,  through  the  dorsal  suture.     Two  branches  are 
given  off  by  this  bundle  not  far  from  the  base  of  the  leaf,  near 
its  two  united  margins,  —  that  is,  at  the  ventral  suture. 

487.  The  folded  carpellary  leaf  has  incurved  margins  ;  so  that 
whatever  the  arrangement  of  the  wood  and  liber  may  be  in  the 
median  line  of  the  leaf,  the  reverse  will  be  found  at  the  margins. 
Thus  in  each  of  the  three  carpels  shown  in  Fig.  133  a,  the  fibro- 


1 


vascular  bundle  running  through  the  dorsal  suture  has  liber  on  its 
outside  (the  unshaded  portion)  and  wood  on  its  inside  (the  dark 
portion).  But  in  each  of  its  branches  at  or  near  the  ventral 
suture  liber  occurs  on  the  inside  (that  is,  nearest  the  centre  of 
the  flower)  and  wood  on  the  outside. 

488.  Compound  Pistils.  If  several  carpels  unite  to  form  a 
compound  ovary,  the  same  inversion  of  the  order  of  the  parts  of 
the  bundles  (as  shown  in  Fig.  133  a)  will  be  seen  when  the 
bundles  at  the  centre  of  such  an  ovary  are  compared  with  those 
at  its  periphery  (see  diagrams  b  to/,  Fig.  133). 

FIG.  133.  Transverse  section  of  superior  ovaries,  showing  the  arrangement  of  the 
flbro-vascular  bundles  of  carpels:  a,  Krai!  this  hyemalis;  6,  Hyacinthus  oriental  is; 
c,  Tulipa  Gesneriana ;  d,  Impatiens  tricornis ;  e,  Anagallia  arvengls;  /,  Lychnis  dloic». 
(Van  Tieghem.) 


174 


MINUTE   STRUCTURE   OF   THE   FLOWER. 


489.  But  if  the  ovaries,  instead  of  being  superior,  as  those  in 
Fig.  133,  are  inferior,  as  those  in  Fig.  134,  further  complications 
are  caused.      The  fibro-vascular  bundles  of  the  several  floral 
whorls  united  with  the  pistil  are  distributed  in  circles  in  the 
parenchyma  tissue  of  the  ovary.     Thus  in  Fig.  134  a,  we  find 
five  such  circles,  corresponding  to  the  cabyx,  corolla,  stamens, 
and  dorsal  and  ventral  sutures  of  the  carpel.     The  bundles  in 
Fig.  134  a  are  arranged  in  radial  lines  from  the  centre  outwards  ; 
the  six  bundles  nearest  the  centre  of  the  ovary  are  those  of  the 
ventral  sutures,  and  have  wood  outside  and  liber  inside  ;  in  the 
next  circle  the  three  with  reverse  arrangement  of  elements  are 
those  of  the  dorsal  sutures  from  which  the  bundles  just  spoken 
of  branched.     In  Fig.  134  #,  all  the  fibro-vascular  bundles  save 

those  of  the  carpels 
are  united  to  form  a 
single  circle,  thus  giv- 
ing rise  to  the  three 
circles  of  bundles 
seen  in  the  cross- 
section,  and  at  the 
base  of  the  ovary 
even  these  did  not 
exist  separate.  In 
Fig.  134  c,  the  bun- 
dles of  all  the  floral 
whorls  are  blended 
for  a  considerable 
height  in  the  ovary  ; 
finally,  the  bundles 
of  the  ventral  sutures 
become  separated 
from  the  rest,  which 
continue  united 
throughout,  forming 

the  large  bundles  seen  on  the  periphery  of  the  ovary  in  Fig. 

134  c.     The  arrangement  of  the  bundles  in  this  figure  should  be 

compared  with  that  in  Fig.  133. 

490.  The  structure  of  the  peduncle  and  the  pedicels  is  sub- 
stantially the  same    as  that  of  the  stem,  and  the  structure  of 

FIG.  134  Transverse  section  of  the  inferior  ovary,  showing  the  arrangement  of  fibro- 
vascular  bundles  both  in  the  carpels  and  the  external  parts  of  the  flower:  o,  Alstrce- 
meria  versicolor,  the  fascicles  of  the  whorls  independent;  b,  Galanthus  nivalis,  the 
fascicles  no  longer  so  distinctly  radial;  c,  Campanula  Medium,  the  fascicles  of  th« 
whorls  blended.  (Van  Tieghem.) 


DEVELOPMENT   OF   THE   OVULE. 


175 


the  bracts  is  much  like  that  of  the  leaf ;  therefore  these  need  not 
be  specially  considered  here. 

491.  Ovules  are  normally  formed  at  definite  points  or  lines 
upon  the  ovarian  wall,  which  answer  to  the  edges  of  the  carpel- 
lary  leaves.     The  funiculus  arises  as  a  slight  elevation  produced 
by  the  multiplication  of  a  cell  or  a  group  of  cells  under  the 
epidermis;  in  the  centre  of  this  elevation,  and  also  under  the 
epidermis,  further  development  produces  a  spheroidal  or  cone- 
like  mass, — the  nucleus.     Then,  a  little  later,  cells  at  the  base 
of  the  nucleus  begin  to  produce  a  cylinder  (the  inner  integu- 
ment), and   shortly  after,  a  second   one  is  formed  below  and 
outside  this  (the  outer  integument).     Subsequent  development 
carries  the  outer  integument  quite  up  and  around  the  inner  one, 
and  the  nucleus;  leaving  a  small  opening  (the  foramen).     For 
peculiarities  in  the  morphology  of  the  ovule,  and  for  cases  in 
which  one  or  both  integuments  may  be  wanting,  see  Volume  I. 
page  278. 

492.  The   funiculus   has  a  collateral  nbro-vascular   bundle, 
having  its  median  plane  coincident  with  that  of  the  ovule.     The 


bundle  is  surrounded  by  parenchyma  and  epidermis.  It  is  fre- 
quently prolonged  into  the  integuments,  being  there  more  or  less 
branched. 

FIG.  135.  Development  of  the  ovule  of  Aristolochia  Clematitis.  A,  young  ovule  in 
vertical  section;  B,  same,  more  advanced;  tl,  internal  integument  forming;  C,  a  later 
stage  of  same;  ti,  internal  integument;  te,  external  integument  forming;  D  and  E, 
later  stages  of  nucleus,  to  be  described  in  Part  II.  (Warming.) 


176  MINUTE   STRUCTURE   OF   THE   FRUIT. 


THE   FRUIT. 

493.  The  fruit  is  the  ripened  pistil.     But,  as  shown  in  Vol- 
ume I.,  "  it  is  a  loose  and  multifarious  term,  applicable  alike  to 
a  matured  ovai-y,  to  a  cluster  of  such  ovaries,  at  least  when 
somewhat  coherent,  to  a  ripened  ovary  with  calyx  and  other 
floral  parts  adnate  to  it,  and  even  to  a  ripened  inflorescence  when 
the  parts  are  consolidated  or  compacted." 

494.  Histologically  considered,  fruits  present  few  difficulties, 
although  the  changes  in  form  which  a  pistil  undergoes  as  it  ripens 
are  not  greater  than  the  changes  which  it  may  suffer  in  minute 
structure.      These  histological  changes  are  referable  to  a  few 
simple  kinds  :  ( 1 )  a  great  development  of  sclerotic  elements,  seen 
in  the  harder  dry-fruits  and  in  the  putamen  of  all  stone-fruits ; 
(2)  a  large  increase  in  the  amount  of  soft-walled  parenchyma, 
containing  sap,  as  in  the  pulp  of  all  fleshy  fruits ;  (3)  a  consid- 
erable development  of  color,  especially  in  the  superficial  parts. 

495.  Sections  to  exhibit  the  structure  of  the  very  hard  parts 
of  fruits  are  made  most  easily  by  carefully  grinding  the  parts 
on  a  fine  oil-stone.     First,  a  fragment  of  the  hard  shell  of  a  nut 
or  of  the  putamen  of  a  drupe  is  obtained  by  means  of  any  strong 
cutting  instrument,  and  a  flat  surface  parallel  to  the  plane  of 
the  section  desired  made  by  a  clean  file.     On  a  glass  slide  a 
drop  of  Canada  balsam  is  placed,  and  heated  until  the  more 
volatile  portion  is  expelled  (see  111).     Then  the  flat  side  of  the 
object  just  prepared  is  held  upon  this  balsam  until  the  latter 
becomes  cool  and  hard ;  and  when  thus  securely  fastened,  the 
specimen  is  rubbed  down  on  an  oil-stone  to  any  required  de- 
gree  of  thinness.      It  is  removable  from  the  slide   by  oil   of 
turpentine,  and  can  afterwards  be  mounted  in  a  fresh  portion  of 
balsam  or  of  benzol-balsam  (see  112). 

496.  The  contents  of  the  parenchyma  cells  of  fruits  depend 
very  largely  on  the  degree  of  maturit}'  of  the  fruit.     Changes  in 
the  contents  go  on  from  the  formation  of  the  fruit  until  it  is  fully 
ripe.     In  some  of  the  more  common  cases  these  consist  largely 
in  the  production  of  various  sugars,  especially  that  which  is 
known  as  fruit-sugar;  and  organic  acids,   for  instance,  citric, 
tartaric,   and  malic  acids.      A  consideration  of  these  changes 
belongs  to  Part  II. 

497.  The  coloring-matters  in  fruits,  like  those  in  flowers,  are 
either  color-corpuscles  (chromoplastids),  or  substances  dissolved 
in  the  cell-sap.     In  a  few  cases  the   walls  of  the  cells   them- 
selves have  more  or  less  color. 


COLORING-MATTERS   OF  FRUITS.  177 

498.  The  berries  of  a  common  house-plant,  JSolanuin  Pseudo- 
capsicum,  furnish  excellent  material  for  the  examination  of  the 
coloring-mutters  of  fruits.      The  following  account,  condensed 
from  Kraus,1  will  show  the  essential  characters  of  the  color- 
granules  in  this  case,  and  it  should  be  compared  with  what  has 
been  already  said  about  the  structure  of  chlorophyll  granules 
and  leucoplastids  (168  et  seq.},  as  well  as  with  the  account  of 
the  chromoplastids  in  the  parts  of  flowers  (477). 

A  section  through  the  ripe  pericarp  shows  that  it  consists  of 
twenty  to  thirty  or  more  layers  of  cells,  in  most  of  which  color- 
granules  occur.  In  the  outermost  cells  the  granules  closely 
resemble  both  in  form  and  structure  ordinaiy  granules  of  chloro- 
phyll. In  some  of  the  granules  the  coloring-matter  is  evenly 
diffused  through  the  whole  mass,  while  in  others  it  is  confined 
to  some  one  part,  the  rest  of  the  granule  remaining  without  color 
of  any  kind.  In  these  cases  the  colored  and  the  uucolored  parts 
are  not  very  sharply  divided  from  each  other. 

499.  Other  granules  less  like  chlorophyll-granules  occur,  in 
which  there  is  a  sharp  demarcation  between  the  colored  and 
uncolored  parts ;    such  have   been  shown  to  be  vacuolar,   the 
vacuoles  assuming  widely  different  shapes.     These  are  abundant 
in  the  cells  which  lie  five  to  eight  layers,  or  rather  more,  from 
the  outside. 

In  some  of  these  the  colored  portion  appears  spindle-form  or 
sickle-form,  in  others  curved  twice,  like  the  letter  S.  It  fre- 
quently happens  that  several  of  these  long  granules  are  placed 
end  to  end,  forming  an  irregular  chain. 

500.  In  the  part  of  the  berry  which  envelops  the  seeds  the 
color-granules  are  extremely  slender,  and  needle-shaped.2     All 
of  the    granules    lie    in   the   protoplasm;    usually   in   greatest 
number  in  that  lining  the  walls,  and  immediately  around  the 
nucleus. 

501.  Occasionally  in  the  larger  pericarp-cells  roundish  col- 
ored objects  are  met  with,  which  close  examination  shows  are 
nothing  but  vacuoles  in  the  protoplasm  of  the  cell  filled  with 
colored   sap;    sometimes    these   have   been   mistaken   for   the 
granules  themselves,  but  they  can  usually  be  distinguished  from 
them  without  difficulty,  on  account  of  the  distortion  which  they 
undergo  upon  slight  pressure. 


1  Kraus:  Pringsheim's  Jahrb.,  1872,  p.  131. 

2  Trecul :  Ann.  des  Sc.  nat.,  ser.  4,  tome  x,  1858,  p.  154.    Weiss:  Site.  d.  k. 
Akad.  Wien,  1864  (Band  1.),  and  1866  (Band  liv.). 

12 


178  MINUTE    STRUCTURE   OF   THE   SEED. 


THE   SEED. 

502.  The  ripened  ovule  is  the  seed.     In  ripening,  the  ovule 
undergoes  changes  in  the  structure  both  of  the  integuments  and 
the  nucleus.     The  integuments  of  the  seed  answer  morphologi- 
cally to  the  prirnine  and  secundine  of  the  ovule  ;  the  outer  being 
the  testa,  or  seed-shell,  —  also  called  spermoderm  or  episperm, 
—  the  inner  the  tegmeu,  or  eudopleura.      The   nucleus  of  the 
seed  also  answers  to  the  nucleus  of  the  ovule.     The  morpho- 
logical relations  of  the  different  parts  of  the  seed  have  been 
sufficiently  treated  in  the  first  volume,  "Structural  Botany,"  and 
therefore  only  the  histological  features  will  now  be  presented. 

503.  Considered  as  a  whole,  the  testa  varies  greatly  in  con- 
sistence ;  it  is  in  some  cases  as  dense  as  an}r  sclerotic  tissue, 
while  in  others  it  is  pulpy,  and  in  others  still,  membranaceons. 
But  it  is  usually  divisible  under  the  microscope  into  two  or  more 
Ia3-ers,  which  are  not  constant  in  their  characters. 

504.  The  ordinary  layers   met  witli   in   the   seeds   of  most 
agricultural  plants  have  been  described  by  Nobbe l  in  the  follow- 
ing terms :    1 .  The  hard  la3Ter,  composed  generally  of  palisade 
or  staff-like  cells  of  considerable  firmness.     In  Leguminosse  it 
is  the  external  layer,  and  its  exposed  surface  is  cuticularized. 
In  flax  and  species  of  Brassica,  it  is  the  second,  in  cabbage 
and  mustard,  the  third  layer.     In  a  few  cases  the  cells  of  this 
layer  are  tabular  instead  of  staff-shaped.     2.  The  mucilaginous 
layer,  not  present  in  all  the  common  agricultural  seeds,  is  com- 
posed of  cells  whose  walls  have  the  power  of  swelling  greatly 
when  the}'  are  placed  in  water.     This  layer  is  sometimes  found 
in  the  outer  part  of  the  testa,  sometimes  in  the  inner.     3.  The 
pigment  Ia3"er,  which  imparts  characteristic  colors  to  the  coats  of 
the  seeds  of  many  plants,  is  not  constant  in  the  form  of  the  cells. 
The  color  may  reside  in  the  cell-wall,  or  in  the  dried  contents  of 
the  cell.     Sometimes  a  few  pigment-cells  are  scattered  among 
others  of  a  neutral  tint,  and  even  among  those  which  cannot  be 
said  to  have  any  proper  color  at  all.     In  some  cases  one  of  the 
other  layers  may  contain  more  or  less  color.     In  a  few  other 
instances  the  color  is  not  dependent  on  a  pigment  laj'er ;  for,  as 
Frank2  has  shown,  in  the  steel-blue  seeds  of  species  of  Paeonia 
the  color  is  purely  a  result  of  reflected  light,  and  is  in  no  wise 
due  to  the  presence  of  anjr  true  coloring-matter.     The  dried 
seeds  are  dark  red  or  dark  brown  ;  hut  when  thoroughly  moist- 

1  Haudbuch  <ler  Samenkunde,  p.  73.  -  Botanische  Zeitung,  1867. 


HAIRS. 


179 


eiied  with  water  (or  better  still  in  a  fresh  state),  they  are  dis- 
tinctly blue.  4.  The  protein  layer,  the  cells  of  which  contain 
granular  albuminoid  matters. 

The  layers  just  described  are  different  in  different  seeds,  aud 
sometimes  different  in 
different  parts  of  the 
same  seed-coat,  so  that 
the  division  has  really 
little  utility. 

505.  The  external  in- 
tegument or  testa  may 
have  well-developed  hairs, 

as  has  been  shown  in  Vol-  M  ^Fs2^.Vrw"3^"^0  Hf 
ume  I.  p.  306.  Only  one 
of  these  cases  of  hairs 
can  be  here  described ; 
namely,  those  which  form 
the  felted  covering  of  cot- 
ton-seeds, and  which  are 
the  "cotton"  of  commerce.  These  are  slender  cells  with  col- 
lapsed walls.  As  they  ap- 
proach maturity,  the  cells 
become  more  or  less  twisted  ; 
the  resulting  spiral  is  that 
which  imparts  to  cotton  its 
value  as  a  material  for  spin- 
ning. Some  other  seeds, 
notably  those  of  species  of 
Asclepias,  have  long  and 
strong  hairs,  but  none  of 
these  have  any  spiral  twist 
which  fits  them  for  textile 
purposes. 

Regarding  the  size  of  cot- 
ton "fibres"   (hairs  of  the 
seed),  the  following  meas- 
urements by  Ordway  are  of  interest :  Maximum  length  in  the 
"sea-island"  variety,  about  two  inches  (five  centimeters);  in 

FIG.  136.  Cross-sections  of  cotton-fibres.  A  A,  immature  fibres;  B  B,  half-mature 
fibres;  C  C,  fully  mature  fibres;  D,  section  of  fibre,  showing  laminated  cell-walls. 
(Bowman.) 

FIG.  137.  A,  Glassy,  structureless  fibre;  B,  thin,  pellucid,  immature  fibre;  C,  half 
mature  fibre,  with  thin  cell-wall ;  D  and  E,  fully  mature  fibre,  with  full  twist  and  well- 
defined  cell-wall.  (Bowman.) 


180  MINUTE  STBUCTURE   OF  THE   SEED. 

upland  or  "short-staple"  cotton,  a  little  over  one  inch  and  a 
half  (three  and  three-fourths  centimeters).  The  greatest  width 
of  fibre  was  found  to  be  .0013  inch.  A  single  fibre  sustained 
without  breaking  a  weight  of  150  grains.1 

506.  It  has  been  shown  in  Volume  I.  that  the  seed-coats  of 
many  Polemoniaceae,  etc.,  are  furnished  with  microscopic  hairs, 
"which  come  usefully  into  play  in  arresting  farther  dispersion  at 
a  propitious  time  or  place.   .   .   .  The  testa  is  coated  with  short 
hairs,  which  when  wetted  burst,  or  otherwise  open  and  discharge 
along  with  mucilage  one  or  more  verj-  attenuated  long  threads 
(spiricles)  which  were  coiled  within.     These  protruding  in  all 
directions,  and  in  immense  numbers,  form  a  limbus  of  considera- 
ble size  around  the  seed,  and  evidently  must  serve  a  useful  end 
in  fixing  these  small  and  light  seeds  to  the  soil  in  time  of  rain, 
or  to  moist  ground,  favorable  to  germination,  to  which  they  ma}' 
be  carried  by  the  wind."     The  best  example  of  this  structure  is 
afforded  by  the  genus  Collomia ;  in  this  the  spiricles  are  long 
and  very  numerous. 

507.  The   nervation  of  the    seed-coats   furnishes  in  many 
cases  excellent  diagnostic  characters,  but  they  need  no  special 
remark  histologically.     The  forms   of  branching  of  the  fibro- 
vascular  bundle  of  the  funicnlus  indicate  that  the  ovule   and 
seed  are  of  the  nature  of  leaflets  on  the  margin  of  the  carpellary 
leaf.8 

1  The  above  measurements  are  approximate ;    those  which  follow  are  the 
exact  determinations  as  they  are  given  by  Professor  Ordway  in  the  Tenth 
Census  of  the  United  States. 

Length  of  fibre.  Maximum  length  found  in  the  "sea-island"  variety  of 
South  Carolina,  where  it  was  1.996  inches.  The  maximum  length  of  the 
upland  or  "short-staple"  cotton  was  1.669  inches.  The  minimum  of  length 
(0.695  inch)  was  found  in  North  Carolina  cotton,  grown  on  a  light,  sandy 
loam  soil. 

Width  of  fibre.  The  widest  d^W  inch  wide)  was  quite  short  (0.945  inch). 
By  far  the  largest  number  of  wide  fibres  come  from  uplands.  The  "sea-island" 
variety  had  a  width  of  ntthe  inch. 

Strength  of  fibre.  The  strongest  specimen  examined  had  a  breaking  weight 
of  149.4  grains.  Professor  Ordway  mentions  some  instances  which  lead  him  to 
think  that  the  strength  of  the  fibre  may  hold  some  relation  to  the  amount  of 
phosphoric  acid  in  the  soil  where  it  is  grown. 

Weight  of  seeds  and  lint.  (Maximum  weight  for  five  seeds  with  lint  at- 
tached, 22.14  grains.)  Light-weight  seeds  appear  to  come  from  sandy  soils, 
heavy-weight  seeds  from  heavy  and  productive  soils. 

2  The  reader  is   referred  to  a  memoir  by  Le  Monnier,  in  Ann.  des  Sc. 
uat.,  ser.  5,  tome  xvi.,  1872,  p.  233,  and  one  by  Van  Tieghem  in  same  Journal, 
1872. 


ALBUMINOUS    AND   EX  ALBUMINOUS   SEEDS. 


181 


508.    The  so-called  ''grains"  of  the  cereals  are  fruits  instead  of 
seeds  ;  the  accompanying  figures  exhibit,  therefore,  not  only  the 

a      b   .  d 


structure  of  the  integuments  of  the  seeds,  but  also  of  the  ripened 
ovarian  wall. 

509.   As  shown  in  the   "  Structural  Botany,"  page  309,  the 
nucleus  of  the  seed  consists  of  the  embryo  and  its  supply  of 
a  b  c  food.     If  the  store  of  food  is  wholly 

within  the  tissues  of  the  embryo,  the 


seed  is  said  to  be  exalbuminous  ;  if  partly  outside  of  the  embryo, 
as,  for  instance,  in  the  cereals  here  figured,  it  is  said  to  be 
albuminous.  The  albumen  is  the  supply  of  food  in  the  nucleus 
of  the  seed  which  is  not  stored  in  the  embryo  itself. 

FIG.  138.  Cross-section  from  the  periphery  of  the  fruit  of  Zea  Mais,  highly  magni- 
fied: a,  fruit-capsule;  b,  seed-coat;  c,  adherent  cellular  layer;  d,  starch  containing 
albumen  of  seed.  (Berg  and  Schmidt.) 

FIG.  139.  A  cross-section  from  the  periphery  of  the  fruit  of  Avena  sativa,  highly 
magnified :  a,  chaff;  b,  fruit-capsule  with  the  seed-coat ;  c.  a-lherent  cellular  layer ; 
d.  starch  containing  albuminoid  parenchyma.  (Berg  and  Schmidt. ) 

FIG.  140.  Cross-section  from  the  periphery  of  the  fruit  of  Oryza  sativa,  highly  mag- 
nified: a,  chaff';  It,  fruit -capsule  with  seed-coat;  c,  adherent  cellular  layer;  d,  starch 
containing  albuminoid  parenchyma.  (Berg  and  Schmidt.) 

FIG.  141.  Cross-section  from  the  periphery  of  the  fruit  of  Hordeum  vuleare,  highly 
magnified:  a,  chaff';  b,  fruit-capsule  with  the  seed-coat;  c,  adherent  cellular  layer; 
d,  starch  containing  albuminoid  parenchyma.  (Berg  and  Schmidt. ) 


182 


MINUTE   STRUCTURE   OF   THE   SEED. 


510.  The  embryo  may  exist  as  a  cluster  of  parenchyma  cells 
without  any  clear  distinction  of  parts,  or  it  may  possess  a  defi- 
nitely formed  axis  and  leaves  (see  "Structural  Botany,"  p.  311). 

The  microscopic  structure  of  the  nucleus  has  been  illustrated 
in  part  by  the  figures  of  the  grains  of  cereals  (see  also  Fig.  22, 
on  page  47),  and  it  has  been  considered  also  to  some  extent  in 
the  descriptions  of  the  nascent  root  and  the  nascent  stem  in  the 
embryo.  The  study  of  the  development  of  the  embryo  within 
the  seed  belongs  to  a  special  subject,  which  will  be  treated  in 
Part  II.  under  "  Reproduction."  It  therefore  will  suffice  here  to 
state  that  the  parenchyma  cells  of  which  the  nucleus  is  composed 
contain  food  materials  and  protein  matters  in  large  amount. 

511.  The  proper  food  materials  in  seeds  are  chiefly  oils  and 
starches.     The  seeds  of  a  large  number  of  plants  have  been  ex- 
amined by  Niigeli1  with  reference  to  the  occurrence  of  starch,  and 
the  following  facts  are  taken  from  his  extensive  treatise :  — 


riiffiiiogams  containing 

Gym  no- 
sperms, 
Families 

Monocoty- 
ledons, 
Families. 

Dicotyle- 
dons, 
Families. 

Total, 
Families. 

fin  all  species    . 
No  starch  in  the  seed  J  g|  J^™11*   ' 

3 

20 

190 
10 
10 

213 
10 
10 

1  In  a  small  number 

1 

3 

Starch  in  the  albumen, 
not  in  the  embryo 

In  all  species     . 
In  a  majority   . 
In  half?  .    .    . 

i 

17 

1 

16 
1 
3 

34 
2 
3 

Starch  in  the  embryo, 
not  in  the  albumen 

In  all  species    . 

2 

2 

In  all  species    . 

4 

11 

15 

Starch  in  the  albumi- 

In a  majority    . 

1 

1 

nous  embryo 

In  half     .     .    . 

5 

5 

In  a  small  number 

13 

13 

Starch  in  the  embryo 

In  all  species    . 

i 

1 

2 

and  albumen 

In  a  majority    . 

1 

1 

|  In  all  species    . 

2 

21 

30 

53 

Starch    in     the    seed  j  In  a  majority    . 

1 

3 

4 

throughout            1  In  half.     .    *    . 

8 

8 

(  In  a  small  number 

.     .    . 

13 

13 

512.  The  protein  granules  in  seeds  are  classified  by  Vines 2  as 
follows :  — 

1  Die  Starkekomer,  1858,  p.  387. 

2  Proceedings  of  the  Royal  Society,  vols.  xxviii.,  xxx.,   and  xxxi.      On 
page  62  of  the  volume  last-  mentioned  the  following  table  of  seeds  and  their 
aleurone  grains  is  given  :  — 

I.  Soluble  in  water  :  Pseonia  officinalis  (type),  Ranunculus  acris,  Aconitum 

Napellus.  Nigella  damascena,  Helleborus  ftetidus,  Amygdalus  com- 
munis,  Prunus  cerasus,  Pyrus  malus,  Leontodon  Taraxacum,  Dipsa- 
cus  Fullonum,  Ipomoea  purpurea,  Phlox  Drummondi,  Vitis  vinifera. 

II.  Completely,  and  more  or  less  readily,  soluble  in  ten  per  cent  NaCl 

solution. 


PROTEIN  GRANULES  IN  SEEDS.          183 

I.  Soluble  in  water;  e.  g.,  Paeonia  offlcinalis. 

II.  Completely,  and  more  or  less  readily,  soluble  in  ten  per 

cent  NaCl  (sodic  chloride)  solution. 

a.  Grains  without  crystalloids. 

(a.)  Soluble  in  saturated  NaCl  solution  after  treatment 
with  alcohol  or  ether ;  e.  g.,  Pisum  sativurn. 

(ft.}  Soluble  in  saturated  NaCl  solution  after  treatment 
with  alcohol,  but  not  after  ether;  e,  g.,  Helianthus 
annuus. 

b.  Grains  with  crystalloids. 

(a.)  Crystalloids  soluble  in  saturated  NaCl  solution  after 
treatment  with  alcohol  or  ether;  e.  g.,  Bertholletia 
excelsa. 

(ft.)  Crystalloids  soluble  in  saturated  NaCl  solution  after 
alcohol  but  not  after  ether  ;  e.  g.,  Ricinus  communis. 


a.  Grains  without  crystalloids. 

(a.)  Soluble  in  saturated  NaCl  solution  after  treatment  with  alcohol  or 
ether  :  Lupinus  hirsutus  (type),  Vicia  Faba,  Pisum  sativum,  Phase- 
olus  multiflorus,  Allium  Cepa,  Iris  pumila  (var.  atrocoerulea),  Colchi- 
cum  autumnale,  Berberis  vulgaris,  Althaea  rosea,  Tropaeolum  majus, 
Mercurialis  annua,  Empetrum  nigrum,  Primula  officinalis. 

(/3.)  Soluble  in  saturated  NaCl  solution  after  alcohol,  but  not  after 
ether  :  Helianthus  annuus  (type),  Platycodon  (Wahlenbergia)  grandi- 
flora,  Sabal  Adaiisoni,  Delphinium  cardiopetalum,  Trollius  Europaeus, 
Actea  sj)icata,  Caltha  palustris,  Aquilegia  vulgaris,  Dianthus  Caryo- 
phyllus,  Brassica  rapa,  Lepidium  sativum,  Medicago  sativa,  Larix 
europsea,  Cynoglossuni  officinale,  Spinacia  oleracea. 

b.  Grains  with  crystalloids. 

(a.)   Crystalloids  soluble   in  saturated  NaCl  solution  after  treatment 
with  alcohol  or  ether  :  Bertholletia  excelsa  (type),  Adonis  autumna- 
lis,  ^Ethusa  Cynapium,  Digitalis  purpurea,  Cucurbita  Pepo. 
(p. )   Crystalloids  soluble  in  saturated  NaCl  solution  after  alcohol,  but 
not  after  ether  :  Ricinus   communis   (type),    Datura   Stramonium, 
Atropa  Belladonna,   Elais  Guineensis,  Salvia  officiualis,  Taxus  bac- 
cata,    Pinus   Pinea,   Cannabis   sativa,   Linum  usitatissimum,    Viola 
elatior,  Ruta  graveolens,  Juglans  regia. 
III.    Partially  soluble  in  ten  per  cent  NaCl  solution. 

a.  Entirely  soluble  in  one  per  cent  sodic  carbonate  solution  :  Pulmonaria 

mollis,  Omphalodes  longiflora,  Borago  caucasica,  Myosotis  palustris, 
Clarkia  pulchella. 

b.  Entirely  soluble  in  dilute  potassic  hydrate. 

(a.)  Grains  without  crystalloids  :  Anchusa  officinalis,  Lithospermum 
officinale,  Echium  vulgare,  Heliotropium  Peruvianum,  Lythrum 
Salicaria. 

(j3. )  Grains  without  crystalloids:  Cupressus  Lawsoniana,  Juniperus 
communis,  Euphorbia  Lathyris. 


184  MINUTE   STBUCTUKE   OF   THE   SEED. 

III.    Partially  soluble  in  ten  per  cent  sodic  chloride  solution. 

a.  Entirely  soluble  in  one  per  cent  sodic  carbonate  solu- 

tion; e.  g.,  Clarkia  pulchella. 

b.  Entirely  soluble  in  dilute  potassic  hydrate. 

(a.)   Grains  without  crystalloids ;  e.  y.,  Ly thrum  Salicaria. 
(ft.)   Grains  with  crystalloids  ;  e.  g.,  Juniperus  communis. 

513.  The  appendages  of  the  seed  known  as  the  strophiole  (at 
the  base  of  the  seed),  the  caruncle  (at  the  micropyle  or  orifice), 
and  the  rnembranaceous  and  pulpy  forms  of  arillus  (see  Vol- 
ume I.  pages  308,  309)  do  not  call  for  further  remark. 

The  separation  of  the  fruit  at  maturity,  and  the  separation  of 
the  ripened  seed  as  well,  are  due  to  changes  analogous  to  those 
described  in  458,  under  the  *•  Fall  of  the  Leaf."  Some  of  the 
special  forms  of  mechanisms  by  which  the  detachment  occurs 
may  be  examined  in  Part  II.,  under  "  Dissemination." 


CHAPTER  V. 

PHYSIOLOGICAL  CLASSIFICATION   OP  TISSUES. 
DIVISION  OF  LABOR  IN  THE  PLANT. 

514.  THE  simplest  plant,  a  green  cell  living  in  water,  pos- 
sesses all  the  appliances  needful  for  the  work  of  vegetation  ; 
namely,  a  protoplasmic  body  containing  chlorophyll,  and  a  cell- 
wall  protecting  it.   It  finds  in  the  water  in  which  it  floats,  and  in 
the  sunlight  to  which  it  is  exposed,  everything  requisite  for  its 
full  activity. 

515.  Its  work  is  twofold  :  First,  that  which  it  does  not  share 
with  the  animal,  and  which  may  therefore  be  called  the  proper 
office  of  the  plant,  —  the  production  of  organic  matter  out  of 
inorganic  materials,  under  the  agency  of  light.      This  work  is 
dependent  upon  the  presence  of  chlorophyll  in  the  cell,  and  is 
known  as  Assimilation.      Second,  that  which  the  animal  like- 
wise can  perform,  —  the  conversion  into  various  forms  of  ac- 
tivity of  the  energy  stored  up  in  food.     This  takes  place  in  the 
protoplasm,  whether  chlorophyll  be  present  or  absent. 

516.  In  a  spherical  cell  isolated  from  others  and  leading  an 
independent  existence,  floating  free  in  the  water,  and  therefore 
presenting  no  one  part  exclusively  to  the  light,  there  is  very 
slight  if  indeed  any  division  of  labor.     One  part  of  its  cellulose, 
protoplasm,  or  chlorophyll  has  the  same  work  to  perform  and  is 
substantially  under  the  same  conditions  as  any  other  part.     But 
if  the  cell  becomes  one  of  many  aggregated  to  form  a  mass  of 
tissue,  its  relations  to  its  surroundings  are  not  the  same  as  be- 
fore, for  its  exterior  is  no  longer  equally  exposed  either  to  water 
or  to  light.    The  cells  in  the  interior  of  such  a  mass  must  derive 
their  supply  of  material  from  without  through  the  agency  of  the 
neighboring  cells ;  hence  division  of  labor  begins.     Inspection 
of  the  mass  shows  that  some  of  its  cells  have  the  office  of  ab- 
sorption, others  that  of  assimilation,  others  that  of  treasuring 
up  the  products  of  manufacture,  etc.     With  this  incipient  divi- 
sion of  labor  there  are  also  notable  changes  in  the  form  of  cells, 
by  which  a  more  complete  adaptation  to  a  particular  kind  of 


186        PHYSIOLOGICAL  CLASSIFICATION   OF  TISSUES. 

work  is  secured.    These  adaptations  are  as  marked  in  the  inter- 
nal anatomy  as  in  the  external  configuration. 

517.  The  parts  of  a  living  being  which  have  definite  kinds  of 
work  to  do  are  known  as  organs 1  (cf.  e/ayov,  work).  Since  they 

1  The  organs  of  the  higher  plants  are  reducible  to  three  members  ;  that  is, 
three  types  of  structure,  which  bear  to  each  other  definite  relations  of  position 
and  sequence  of  appearance.  These  members  are  the  root,  stem,  and  leaf,  —  to 
which  some  add  also  the  plant- hair.  In  Sachs's  Vorlesungeu,  the  number  of 
members  is  given  as  two  ;  namely,  root  and  shoot. 

In  their  very  youngest  state  all  the  modified  leaves  upon  a  given  plant  are 
indistinguishable  from  each  other ;  the  leaves  which  are  to  become  petals, 
stamens,  leaf-traps,  or  tendrils,  are  like  those  which  are  to  be  ordinary  foliage. 
The  same  is  true  of  modified  stems  and  modified  roots  ;  however  diverse  in 
shape  and  function  the  modified  stems  or  branches  of  a  plant  may  finally  be, 
they  are  at  their  very  beginning  precisely  alike. 

In  the  determination  of  the  rank  of  an  organ,  that  is,  its  reference  to  one  of 
the  three  plant-members  already  enumerated,  the  following  criteria  are  em- 
ployed :  (1)  its  position  with  respect  to  other  parts  ;  (2)  its  nascent  condi- 
tion ;  (3)  its  presence  or  absence  in  organisms  obviously  allied  to  the  one  in 
which  it  occurs,  its  rank  in  these  not  being  obscure. 

So  far  as  the  organs  seen  by  the  naked  eye  are  concerned,  it  is  seldom  that 
any  serious  difficulty  exists  in  the  application  of  at  least  one  of  these  criteria 
to  the  determination  of  their  rank,  and  it  is  generally  possible  to  use  more 
than  one.  But  it  is  different  in  the  case  of  the  histological  organs,  for  (1)  the 
position  can  be  made  out  only  in  sections  of  the  given  part ;  (2)  their  early 
nascent  condition  is  the  simple  cell,  common  to  all  tissues  ;  (3)  it  is  not  easy 
to  determine  whether  an  organ  exists  in  a  rudimentary  form  in  allied  organisms 
or  is  wholly  absent  from  them. 

It  is  so  difficult  to  apply  these  criteria  to  the  study  of  tissues,  and  the 
results  obtained  are  so  contradictory,  that  there  is  no  complete  agreement 
among  botanists  as  to  what  constitutes  a  histological  member  except  the  sim- 
ple cell  itself.  In  fact,  as  stated  in  191,  it  is  doubtful  whether  with  the 
material  now  at  hand  it  would  be  possible  to  construct  a  satisfactory  system 
of  tissue  elements  or  histological  organs  upon  a  purely  morphological  basis. 
Even  in  the  systems  which  most  nearly  approach  this  there  are  some  physio- 
logical notions  which  have  affected  a  few  of  the  minor  divisions. 

A  classification  of  tissues  upon  the  basis  of  physiology  alone  is  open  to 
serious  objections  ;  one  kind  of  work  in  the  plant  can  be  performed  by  diverse 
tissues,  and  on  the  other  hand  one  kind  of  tissue  can  perform  more  than  one 
kind  of  work.  This  is  illustrated  by  the  structural  elements  through  which 
mechanical  ends  are  reached  ;  the  long  bast-fibres,  woody  fibres,  collenchyma, 
and  short  sclerotic  parenchyma,  —  very  diverse  elements,  but  accomplishing  the 
same  result.  Yet  one  of  these,  namely,  the  woody  fibres,  is  among  the  most 
important  of  the  elements  by  which  crude  liquids  are  carried  through  the 
plant. 

Moreover,  in  the  examination  of  the  minute  structure  of  a  part  it  is  not 
easy  to  discriminate  between  the  different  offices  which  one  of  its  given  ele- 
ments may  fill,  because  the  element  is  associated  with  so  many  others  in  the 
formation  of  a  complex  organ. 


DIVISION    OF    LABOR    IN    THE   PLANT.  187 

are  parts  of  a  whole,  —  the  organism,  —  they  must  have  definite 
relations  to  each  other  as  regards  position  and  office. 

518.  The  relations  of  origin  and  position,  so  far  as  the  organs 
of  the  plant  are  concerned,  are  discussed  in  the  first  volume ; 
the  relations  of  origin  and  position  of  the  component  parts  of 
their  structure  have  occupied  the  earlier  portion  of  the  present 
volume.     From  a  review  of  the  facts  there  presented,  it  appears 
that  any  given  part  may  subserve  different  ends  ;  for  instance,  a 
leaf  may  carry  on  its  proper  work,  namely,  that  of  assimilation, 
and  at  the  same  time  may  aid  as  a  tendril,  and,  in  the  case  of 
Nepenthes,  as  a  stomach  for  digestion.     On  the  other  hand,  it 
is  equally  clear  that  the  same  kind  of  work  may  frequently  be 
performed  by  different  parts.     For  instance,  the  proper  work  of 
the  leaf  can  be  carried  on  by  any  green  tissue  ;  not  merely  in 
proper  leaves,  but  in  the  cortex  of  young  stems,  and  even  in  the 
outer  tissues  of  young  roots  of  certain  aerial  plants.    It  is  there- 
fore sometimes  advantageous  in  Vegetable  Physiolog3r  to  distin- 
guish between  systems  of  tissues  having  different  offices,  rather 
than  between  organs  which  are  often  masses  of  heterogeneous 
tissues. 

519.  Among  the  systems  of  classifications  of  tissues  chiefly 
upon  a  physiological  basis  is  that  of  Haberlandt,  which  is  as 
follows :  — 

A.  The  Protective  System. 

1.  Of  the  surface  (Epidermis,  cork,  and  bark). 

2.  Of  the  skeleton  (Bast-fibres,  libriform  cells,  collenchyma, 

and  sclerotic  parenchyma). 

B.  The  Nutritive  System. 

1.  Absorbing  system  (Epithelium  of  roots  and  the  root- 

hairs  ;  absorbing  tissue  of  haustoria,  etc.). 

2.  Assimilating  system  (Chlorophyll  parenchyma,  both  pali- 

sade and  spongy). 

3.  Conducting   system  (Conducting  parenchyma,    vascular 

bundles,  latex  cells  and  tubes). 

4.  Storing  system   (Reserve-tissues  of  seeds,   bulbs,  and 

tubers  ;  water- tissue,  etc.). 

5.  Aerating  system  (Aeriferous  intercellular  spaces,  together 

with  their  external  openings,  stomata  and  lenticels). 

6.  Receptacles  for  secretions  and  excretions  (Glands,  oil, 

resin,  and  mucus  canals,  crystal-sacs,  etc.). 

To  these  might  be  added  the  groups  of  tissues  concerned  in 
reproduction. 


188        PHYSIOLOGICAL   CLASSIFICATION    OF   TISSUES. 


MECHANICS  OF  TISSUES. 

520.  In  Haberlandt's  classification  1  the  tissues  having  a  me- 
chanical office  to  fill  are  brought  into  one  group,  which  is  then 
subdivided  into  (1)  those  tissues  which  protect  the  sorter  tissues 
of  the  interior  from  the  harm  which  would  result  from  exposure, 
and  (2)  those  which  hold  the  soft  tissues  in  place.     An  exami- 
nation of  the  work  performed  by  tissues  may  accompanjr  an  in- 
vestigation of  the  work  by  organs  themselves ;  in  the  examina- 
tion of  the  work  of  organs  in  Part  II.  the  necessary  facts  relative 
to  their  structure  will  be  presented. 

521.  Those  tissues  which  serve  simply  to  impart  strength  to 
the  plant  belong  almost  as  much  to  lifeless  as  to  living  parts,  and 
can  best  be  examined  before  the  subjects  of  physiology  are  taken 
up.     The  present  division  has  for  its  object  the  consideration  of 
that  which  in  Haberlandt's  classification  is  called  the  skeleton, 
and  which  is  known  to  serve  chiefly  mechanical  ends. 

522.  In  the  case  of  a  water-plant,  for  instance  an  alga,  which 
has  about  the  same  specific  gravit}r  as  the  water  in  which  it  is 
borne,  no  special  mechanical  support  is  demanded.     Its  own 
buoyancy  suffices  to  keep  the  structure  as  a  whole  in  place ; 
while  the  different  parts  of  the  simple  organism  have  a  degree  of 
stability  which  enables  them  to  resist  the  action  of  the  waves. 
As  might  be  expected,  such  an  organism  can  attain  a  very  great 
size ;  for  instance,  Macrocystis  pyrifera  of  the  Southern  Pacific 
Ocean  has  been  known  to  measure  nearly  one  thousand  feet,  and 
less  trustworthy  measurements  have  been  recorded  which  far 
exceed  this.     In  this  and  other  water-plants  the  medium  which 
buoys  the  plant  up  takes  the  place  practically  of  any  internal 
framework. 

523.  A  land-plant,  existing  in  a  far  lighter  medium  than  the 
water-plant,   must  have  a  definite  mechanical  support.     Those 
species  of  Calamus  which  furnish  the  "  rattan  "  of  commerce  pos- 
sess a  terminal  shoot  from  which  are  unfolded  in  rapid  succession 
strong  leaves  armed  with  recurved  hooks.     Having  reached  the 
thickly  clustering  tops  of  a  tropical  forest,  the  terminal  bud  de- 
velops its  leaves,  and  these  cling  with  tenacity  to  the  branches 
upon  which  they  rest,  so  that  the  mechanical  support  is  afforded 
in  this  case  by  the  vegetation  beneath.     Thus  supported,  the  ex- 
tension of  the  shoot  is  indefinite,  so  that  examples  of  Calamus 


Phyaiologische  Pflanzenanatomie  (Leipzig,  1884). 


MECHANICAL   ELEMENTS   OF   PLANTS.  189 

with  a  length  of  300  feet  are  not  uncommon,  and  some  figures 
much  higher  than  this  are  noted. 

524.  In  both  the  above  cases  the  extraordina^  size  has  been 
attained  with  very  little  expenditure  of  material  for  mere  me- 
chanical support.     The  same  is  true,  although  in  a  less  striking 
because  a  more  familiar  manner,  in  our  ordinary  twining  and 
climbing  plants  ;  other  plants  or  outside  supports  of  some  kind 
being  necessary  to  bring  their  steins  and  leaves  into  the  best 
relations  to  their  surroundings.     But  what  tissues  serve  to  keep 
erect  or  in  position  the  larger  plants  which  are  not  water-plants 
or  climbers?     What  tissues  serve  mainly  mechanical  ends? 

525.  The   subject  was   extensively   investigated,  so  far  as 
monocotyledonous  plants  are  concerned,  by  Schwendener,1  in 
1874,  since  which  time  some  important   additions  have   been 
made.     According  to  Schwendener,  the  mechanical  elements 
in  the  plant  are  (1)  bast-fibres,  (2)  libriform  cells  and  fibres, 
(3)   collenchyma  cells.     That  these  are  the  chief  elements  of 
strength,  especially  in  monocotyledonous  plants,  appears  from 
his  instructive  experiments,  which  have  been  repeated  by  others. 
Strips,  150  to  400  mm.  in  length  and  about  2  to  5  mm.  wide,  were 
carefully  taken  from  stems  or  leaves  and  immediately  fastened 
in  a  vise  at  one  end,  the  other  end  being  firmly  grasped  by  strong 
pincers  to  which  weights  could  be  attached  at  will.     Behind  a 
strip,  vertically  suspended  from  the  vise,  a  measuring-bar  was 
placed,  so  that  any  elongation  of  the  strip  under  tension  could  be 
accurately  measured.   After  the  apparatus  was  properly  adjusted, 
a  small  weight  was  attached  to  the  pincers,  the  elongation  of 
the  strip  observed,  and  the  weight  then  removed  in  order  to  see 
whether  the  strip  recovered  its  original  length.     Up  to  a  certain 
point  the  recover}'  was  found  to  be  complete  ;  beyond  this  point 
the  elasticity  was  lost,  and  not  again  regained. 

526.  Strips  from  the  middle  part  of  the  leaf  of  Phormium 
tenax,  390  mm.  long  and  1.5  to  2  mm.  wide,  were  placed  in  the 
apparatus  and  subjected  to  the  action  of  a  weight  of  10  kilograms. 
They  became  5  mm.  longer,  but  on  removal  of  the  weight  were 
found  to  recover  their  original  length  ;  in  other  words,  they  re- 
mained  perfectly  elastic   under  this  weight.      A  weight  of   15 
kilograms  broke  the  strips  into  two  parts.     These  strips  con- 
tained only  five  fibro-vascular  bundles,  with  an  amount  of  bast 
which  was  believed  to  be  about  half  a  square  millimeter  in  cross- 


1  Das  mechanische  Princip  ira  anatomischen  Bau  der  Monocotylen  (Leipzig, 
1874). 


190        PHYSIOLOGICAL   CLASSIFICATION   OF   TISSUES. 


section.  From  this  experiment  Schwendener  places  the  strength 
of  the  bast  of  Phormium  tenax  at  20  kilograms  per  square  milli- 
meter.1 

527.  The  tables  in  the  notes  show  that  good  bast  equals  good 
iron  in  its  tensile  strength  within  the  limits  of  elasticity,  while  in 
its  breaking-weight  it  is  greatly  exceeded  by  the  latter.  Schwen- 
dener well  remarks  that  Nature  has  given  her  whole  care  to  pro- 
viding that  these  mechanical  elements  should  be  strong  within 
the  limits  of  elasticity,  and  with  good  reason  ;  for  beyond  those 
limits  the  plant  gains  nothing  by  greater  strength.  Attention  is 
called  also  to  the  great  difference  between  bast  and  the  metals 
with  regard  to  their  elongation  under  weight. 

1  The  results  of  experiments  made  with  the  bast  of  various  plants  iii  the 
manner  described  are  given  below.  Most  of  the  cases  cited  are  from  Schwen- 
dener ;  others  are  from  Haberlandt  (Physiologische  Pilanzenanatomie,  p.  105). 
The  determinations  for  metals  are  from  Weisbach. 


Name. 

Elongation 
in  1000  parts. 

Tensile  strength  in 
kilograms  per  sq. 
mm.  (within  limits 

Breaking- 
weight  in 
kilograms 

of  elasticity). 

per  sq. 
mm. 

Phormium  tenax   .    ,    

13. 

20. 

25. 

14. 

16. 

Fritillaria  imperialis 

12 

Lilium  auratum     

7.6 

19. 

126 

20 

13.3 

178 

21  6 

Dracaena  indivisa  

17. 

17. 

21.8 

12  3 

16  3 

14.7 

17  6 

Polytrichum  juniperinum  (stem)   .    . 

.... 

7.5 

•'            (seta)     .    . 

11.6 

Papyrus  antiquorum      
Molinia  ccerulea     

15.2 
11. 

22! 

Pincenectia  recurvata    

14.5 

25. 

Dianthus  capitatus    
Secale  cereale    

7.5 
4.4 

14.3 
15  to  20 

These  should  be  compared  with  the  results  of  determinations  made  with 
other  materials  :  — 


Name. 

Elongation  in 
1000  parts. 

Tensile  strength 
per  sq.  mm. 

Break  ing-  weight 
in  kilograms. 

Malleable  iron  in  rods     .... 
"    in  wire     .... 
"          "    in  plate    .... 
Hammered  German  steel    .    .    . 
Brass  . 

.67 
1.00 
.80 
1.20 
.75 
135 
.24 
1.00 

13.13 
21.9 
14.6 
24.6 
4.85 
13.3 
2.3 
12.1 
11. 

40.9 
82. 

29. 

Brass  wire  

Copper  wire 

silver  !'!':: 

STEREOM   AND   MESTOM.  191 

528.  The  strength  of  other  tissues  besides  bast  has  been  meas- 
ured ;  thus  Ambronn  assigns  to  collenchyma  a  breaking-weight  of 
12  kilograms  per  square  millimeter,  and  these  cells  become  per- 
manently elongated  under  a  weight  of  from  1.5  to  2  kilograms. 

Haberlandt  found  that  the  breaking-weight  of  the  internal 
"  thread  "  of  the  common  graybeard  lichen,  Usnea  barbata,  is 
1.7  kilograms  per  square  millimeter,  but  that  this  thread  could  be 
stretched  to  double  its  length  before  breaking.  The  breaking- 
weight  of  cotton  fibre  is  calculated  to  be  between  18  and  20 
kilograms  per  square  millimeter,  and  that  of  the  seed-hair  of 
Asclepias  Syriaca  not  far  from  40  kilograms. 

529.  Examination   of  any  of  the   figures  of  fibro-vascular 
bundles  given  in  Part  I.  shows  how  well  their  elements  are  dis- 
tributed in  order  to  secure  the  greatest  strength  with  economy  of 
material.    To  the  elements  which  impart  strength  to  a  bundle 
Schwendener  has  given  the  name  stereom  ;  to  the  other  parts  of 
the  bundle,  mestom  ;  thus  the  fibres  are  stereom  elements,  the 
ducts  are  mestom  elements. 

530.  The  striking  adaptations1  of  the  fibro-vascular  bundles 
to  serve  as  light  and  very  strong  building  materials  in  the  plant 

1  The  following  table  from  Schwendener,  with  a  few  illustrative  examples, 
is  given  to  serve  as  a  guide  to  the  student  in  tracing  out  a  few  of  these  adapta- 
tions :  — 

DISTRIBUTION  OF  MECHANICAL  ELEMENTS  IN  MONOCOTYLEDONS. 

I.    In  cylindrical  organs. 

1.  System  of  subepidermal  nerves  of  bast.     Simple  fascicles  of  bast  lie 

under  the  epidermis. 
First  type.     Arum,  Arisaema. 
Second  type.     Petioles  of  Colocasia  and  Alocasia. 

2.  System  of  compound  peripheral  girders.    Subepidermal  fascicles  of  bast 

unite  with  those  which  lie  more  deeply  to  form  girders  in  which 
the  "web"  or  binding-tissue  is  partly  mestom,  partly  parenchyma. 

Third  type.     Stems  of  Scirpus  csespitosus  and  Eriophorum  alpinum. 

Fourth  type.     Stems  (above  ground)  of  Cyperus  alternifolius. 

Fifth  type.     Stems  of  Schcenus  nigricans. 

Sixth  type.     Stems  of  Juncus  effusus. 

Seventh  type.     Carex  lupulina. 

Eighth  type.     Scirpus  lacustris. 

Ninth  type.     Isolepis  pauciflora. 

Tenth  type.     Cladium  Mariscus. 

8.    System  characterized  by  a  nerved  hollow   cylinder,   the  nerves  of 
which  are  united  with  those  at  the  epidermis. 

Eleventh  type.     Many  grasses  ;  e.  g.,  Alopecurus  pratensis. 

Twelfth  type.     Panicum  Crus-galli. 
4.   System  of  peripheral  bast-fascicles  strengthened  by  mestom. 

Thirteenth  type.     Zea  Mais. 


192       PHYSIOLOGICAL  CLASSIFICATION   OF  TISSUES. 

are  seen  plainly  when  the  distribution  of  the  bundles  in  the  stems 
of  monocotyledons  is  examined  in  cross-section.  In  many  cases 
the  shape  of  the  section  of  the  bundle  is  nearly  that  of  the 
well-known  "  I "  or  "  H  "  beam  or  girder.  In  the  most  clearly 
marked  instances  the  stereom  portion  is  well  developed  on 
both  sides  of  the  mestom,  and  thus  forms  the  "flanges"  or 
"plates,"  while  the  mestom  is  the  "web;"  the  stereom  has 
therefore  to  bear  either  compression  or  tension,  according  to 
the  bending  of  the  part.  It  will  further  be  observed  that  in  all 
cases  the  beam  is  placed  with  respect  to  the  rest  of  the  stem,  so 
as  to  insure  the  greatest  efficiency  of  the  stereom  portion. 

But  it  is  only  upon  a  careful  examination  of  the  man}'  methods 
of  arrangement  of  the  stereom  and  mestom  in  the  bundles 
of  diverse  forms  of  dicotyledonous  stems,  together  with  an  ex- 
amination of  the  arrangement  of  the  bundles  themselves  with 
respect  to  the  surrounding  tissues,  that  the  adaptations  of  the 
various  elements  to  strength  can  be  fully  appreciated. 

The  modes  of  distribution  of  the  stereom  and  mestom  met 
with  in  monocotyledons  are  so  numerous  that  they  cannot  be 
reduced  to  a  few  types ;  their  diversity  is  so  great  that  they  can 
only  with  difficulty  be  brought  into  any  S3rstem  of  classification. 


6.   System  of  subcortical  fibro- vascular  bundles  with  strongly  marked 

bast  development. 

Fourteenth  type.     Bambusa  species. 
Fifteenth  type.     Palms. 
Sixteenth  type.     Yucca. 
Seventeenth  type.     Musa. 
Eighteenth  type.     Maranta. 

6.  System  of  subcortical  fibro-vascular  bundles  united  tangentially. 
Nineteenth  type.     Juncus  GerardL 

7.  System  characterized  by  a  simple  hollow  cylinder  with  imbedded  or 

attached  fascicles  of  Mestom. 
Twentieth  type.     Commelynacese. 
II.    In  bilateral  organs. 

1.  System  of  subepidermal  girders. 
First  type.     Leaves  of  Cyperus. 

Second  type.     Middle  part  of  leaves  of  Zea. 
Third  type.     Leaves  of  Musa. 
Fourth  type.     Leaves  of  Tradescantia. 
Fifth  type.     Leaves  of  Pardanthus. 

2.  System  of  internal  girders. 

Sixth  type.     Leaves  of  Cypripedium. 
Seventh  type.     Petiole  of  Aspidistra. 

8.  System  of  complex  girders  :   subepidermal  nerves  of  bast  combined 

with  interior  girders. 
Eighth  type.     Petioles  of  many  palms. 


>'HY  BIOLOGICAL   CLASSIFICATION   OP   TISSUES.       103 

531.  The  distribution  of  material  in  the  skeleton  of  a  ligneous 
dicotyledonous  plant  is  somewhat  different  from  that  in  a  mono- 
cotyledon.1    More  of  the  mechanical  work  falls  on  the  proper 
wood,  but  even  here  in  some  cases  the  bast  serves  an  important 
purpose. 

532.  The  data  for  calculating  the  strength  of  the  wood}'  stem 
and  branches  of  a  dicotyledonous  plant  are  to  be  found  in  vari- 
ous works  on  mechanical  engineering ;  but  it  is  to  be  borne  in 
mind  that  the  figures  given  for  timber  are  usually  based  on  ex- 
periments with  dry  heart-wood. 

533.  The  trunk  is  to  be  regarded  as  a  column  bearing  the 
weight  of  the  whole  crown  of  branches,  each  of  these  being  a 
tapering  beam  supported  at  one  extremity.    The  crushing-weight 
the  crown  exerts  upon  this  column  is  far  within  the  limits  of 
safety,  even  when  the  liability  of  the  trunk  to  be  much  bent  and 
twisted  by  high  winds  is  taken  into  account.     The  branches  at 
their  point  of  union  with  the  trunk  form  different  angles  in 
different  plants,2  and  this  angle  must  be  taken  into  consideration 

1  DISTRIBUTION  OF  MECHANICAL  ELEMENTS  IN  DICOTYLEDONS. 

1.  With  bast  in  the  bark. 

First  group.     Axial  organs  when  young  have  an  unbroken  ring  of  bast ; 

in  much  older  steins  this  is  interrupted  or  cast  off.     Aristolochia. 
Second  group.      Axial  organs  with  a  layer  of  bast-bundles  which  is 

thrown  off  later.     The  bast-bundles  form  the  first  mechanical  system, 

which  is  soon  replaced  by  the  ring  of  wood.     Nerium  Oleander. 
Third  group.     With  simple  ring  of  bast-bundles  in  first  year,  later  with 

isolated  bast- fibres.     jEsculus  Hippocastanuin. 
Fourth  group.     With  strong  bast,  even  when  far  advanced.     Tilia. 
Fifth  group.     With  subepidermal  bast-nerves.     Russelia. 

2.  With  transition  to  an  intra-cambium  ring  of  libriform  cells. 

Sixth  group.     The  cambium  of  the  bundles  lies  partly  outside,  partly 

inside  the  mechanical  ring,  or  is  imbedded  therein.     Gaillardia. 
Seventh  group.     Isolated  vascular  bundles.     Silphium  perfoliatum. 

3.  Intra-cambium  libriform  ring  without  medullary  rays. 

Eighth  group.     Without  bast  on  the  outer  side  of  the  cambium  or  cam- 

biform  layer.     Impatiens  Nolitangere. 
Ninth  group.     With  larger  or  smaller  amounts  of  bast  on  the  outer  side 

of  the  cambriform.     Urtica  dioica. 
Tenth  group.     In  the  libriform  elements  all  shades  of  transitions  to 

ducts.     Mirabilis  Jalapa. 

4.  Intra-cambium  libriform  ring  with  parenchyma  rays. 
Eleventh  group.     Rays  formed  of  elongated  cells.     Vinca  major. 
Twelfth  group.     Typical  dicotyledons  with  medullary  rays. 

2  McCosh  has  given  the  angles  in  a  large  number  of  plants,  a  few  of  which 

are  here  cited  :  Ash,  60°;  horse-chestnut,  50° -55°;  alder,  50°;  elm,  50°;  oak, 

large  branches,  50°,  small  branches,  65°-  70°  ;  beech,  45°;  linden,  40°.  He  calls 

attention  to  the  fact  that  in  these  and  many  other  cases  the  angle  at  which  the 

13 


194        PHYSIOLOGICAL   CLASSIFICATION   OF   TISSUES. 

in  determining  the  actual  force  exerted  upon  the  fibres  at  the 
base  of  the  branch.1 

534.  The   part  which   sclerotic   parenchyma   and   thickened 
epidermal  and  hypodermal  cells  play  in  affording  strength  to 
plants   need   only  be   alluded  to   (see  211).     In  a  few  cases, 
especially  in  some  succulents,  a  considerable  share  of  the  me- 
chanical support  of  the  plant  is  afforded  by  the  more  superficial 
parts.2 

535.  The  veining  of  leaves  and  the  structure  of  leaf-margins 
present  some  interesting  problems.    Comparative  investigations 3 
have  shown  that  strength  at  the  edge  of  the  leaf  is  obtained  in 
very  different  ways,  even  in  closely  allied  plants.     The  resist- 
ance to  tearing  which  is  exhibited  by  some  of  the  larger  leaves 
of  dicotyledons  is  remarkable. 

The  distribution  of  the  strong  ribs  in  the  leaves  of  the  greater 
water  lilies  (for  instance,  Victoria  regia),  and  to  a  less  striking 
extent  that  in  the  smaller  water  lilies  of  cold  climates,  secures 
great  strength  with  the  utmost  economy  of  material. 

The  trunks  of  many  tropical  trees  are  provided  with  lateral  pro- 
jections (buttresses)  which  strengthen  the  stem  very  materially.4 

veinlets  come  off  from  the  midrib  is  the  same  as  that  formed  by  the  branch  and 
the  trunk.  The  angles  in  the  above  cases  are  those  formed  above  the  points 
where  the  branches  arise  (British  Assoc.  Report,  1852,  part  ii.  p.  68). 

1  Very  instructive  illustrations  of  the  different  capacity  of  different  trees  to 
resist  the  action  of  high  winds  are  given  in  the  Reports  of  the  Signal  Service. 

2  Full  and  interesting  accounts  of  the  adaptations  of  the  framework  to  the 
external  conditions  of  plants  are  to  be  found  in  the  works  of  Schwendener  and 
Haberlandt. 

8  Westermaier  :  Monatsber.  der  k.  Akad.  d.  Wissenschaften  Berlin,  1881. 

*  "  All  are  tall  and  upright  columns,  but  they  differ  from  each  other  more 
than  do  the  columns  of  Gothic,  Greek,  and  Egyptian  temples.  Some  are 
almost  cylindrical,  rising  up  out  of  the  ground  as  if  their  bases  were  concealed 
by  accumulations  of  the  soil ;  others  get  much  thicker  near  the  ground  like 
our  spreading  oaks  ;  others  again,  and  these  are  very  characteristic,  send  out 
towards  the  base  flat  and  wing-like  projections.  These  projections  are  thin 
slabs  radiating  from  the  main  trunk,  from  which  they  stand  out  like  the  but- 
tresses of  a  Gothic  cathedral.  They  rise  to  various  heights  on  the  tree,  from 
five  or  six  to  twenty  or  thirty  feet ;  they  often  divide  as  they  approach  the 
ground,  and  sometimes  twist  and  curve  along  the  surface  for  a  considerable 
distance,  forming  elevated  and  greatly  compressed  roots.  These  buttresses  are 
sometimes  so  large  that  the  spaces  between  them  if  roofed  over  would  form 
huts  capable  of  containing  several  persons.  Their  use  is  evidently  to  give  the 
tree  an  extended  base,  and  so  assist  the  subterranean  roots  in  maintaining  in 
an  erect  position  so  lofty  a  column,  crowned  by  a  broad  and  massive  head  of 
branches  and  foliage  "  (Wallace  :  Tropical  Nature,  1878,  p.  30). 


PART   II. 


CHAPTER   VI. 

PROTOPLASM  AND  ITS  RELATIONS  TO  ITS  SURROUNDINGS. 

536.  UPON   the   framework   which   imparts   strength   to   the 
plant  the  active,-  living  cells  are  distributed.     In  old  ligneous 
dicotyledonous  plants  the  living  parts  are  relatively  so  super- 
ficial that  they  have  been  said  to  form  a  mere  film  of  living 
tissue  held  in  place  by  a  dead  skeleton.1 

537.  The  living  cells  are  those  which  contain  protoplasm. 
Each  of  these  cells  has  definite  relations  to  the  neighboring  cells, 
most  of  which  relations  have  been  presented  in  Part  I.    But  each 
of  these  cells  has  also  definite  relations  to  the  external  world, 
which  it  is  the  province  of  Physiology  to  investigate.     Such  an 
investigation  naturally  begins  with  a  consideration  of  the  char- 
acter of  protoplasm. 

1  "The  living  parts  of  a  tree  or  shrub,  of  the  exogenous  kind,  are  obviously 
only  these  :  1st,  The  summit  of  the  stem  and  branches,  with  the  buds  which 
continue  them  upwards,  and  annually  develop  the  foliage.  2d,  The  fresh 
roots  and  rootlets  annually  developed  at  the  opposite  extremity.  3d,  The 
newest  strata  of  wood  and  bark,  and  especially  the  interposed  cambium -lay  er^ 
which,  annually  renewed,  maintain  a  living  communication  between  the  root- 
lets on  the  one  hand  and  the  buds  and  foliage  on  the  other,  however  distant 
they  at  length  may  be.  These  are  all  that  are  concerned  in  the  life  and  growth 
of  the  tree  ;  and  these  are  annually  renewed.  .  .  .  The  plant  is  a  composite 
being,  or  community,  lasting,  in  the  case  of  a  tree,  through  an  indefinite  and 
often  immense  number  of  generations.  These  are  successively  produced,  en- 
joy a  term  of  existence,  and  peiish  in  their  turn.  Life  passes  onward  con- 
tinually from  the  older  to  the  newer  parts,  and  death  follows,  with  equal  step, 
at  a  narrow  interval.  No  portion  of  the  tree  is  now  living  that  was  alive  a 
few  years  ago  ;  the  leaves  die  annually  and  are  cast  off,  while  the  internodes  or 
joints  of  the  stem  that  bore  them,  as  to  their  wood  at  least,  buried  deep  in  the 
trunk  under  the  wood  of  succeeding  generations,  are  converted  into  lifeless 
heart-wood,  or  perchance  decayed,  and  the  bark  that  belonged  to  them  is 
thrown  off  from  the  surface.  It  is  the  aggregate,  the  blended  mass  alone,  that 
long  survives"  (Gray's  Structural  Botany,  pp.  83,  84.) 


196  PROTOPLASM. 

538.  Protoplasm,  the  living  matter  of  the  plant,  can  be  ex- 
amined to  advantage,  either  as  it  exists  without  a  cell-wall  in 
some  of  the  lower  organisms  (Myxomycetes) ,  or  confined  within 
a  transparent  cell-wall,  as  in  young  plant-hairs. 

539.  The  Myxomycetes  live  in  the  interstices  of  moist  porous 
substances  ;  for  instance,  decaying  leaves  and  stems,  spent  tan, 
etc.     Passing  over  all  details  regarding  their  fructification,  —  a 
subject  to  be  looked  for  in  the  volume  on  "  Cryptogamic  Botany," 
—  their  present  examination  can  begin  with  the  period  when  the 
germinating   spores  of  these   plants   rupture    their  walls,   and 
become  confluent  as  masses  of  naked  protoplasm  known  as 
plasmodia. 

540.  The  plasmodium  of  JEthalium  septicum  is  not  difficult 
to  procure,  as  it  occurs  in  summer  upon  heaps  of  moist  tan  in 
the  open  air,   and  even  during  the  winter  in  moist  places  in 
greenhouses  where  tan  is  used  as  a  stratum  for  flower-pots.     It 
is  a  soft,  gelatinous  mass  of  yellowish  color,  sometimes  measur- 
ing several  inches  in  diameter.     Removal  of  any  portion  of  this 
mass  to  a  glass  slide  is  apt  to  break  up  the  plasmodium  so  much 
as  to  render  it  useless  for  observation  ;  therefore  the  following 
explicit  directions  given  by  Strasburger  for  obtaining  small  por- 
tions to  examine  will  be  found  useful.     A  tumbler  is  to  be  filled 
with  water  up  to  the  brim,  and  from  the  brim  a  strip  of  moist 
filtering-paper,  somewhat  less  than  an  inch  in  width  and  one  or 
two  inches  in  length,  is  to  be  stretched  to  the  cop  of  a  glass  slide 
placed  in  a  vertical  position  (or,  better,  leaning  a  little  out- 
wards) ;  the  lower  end  of  the  slide  being  placed  in  sand  to  catch 
the  water  which  will  soon  begin  to  flow  slowly  over  its  surface. 
Next,  a  piece  of  bark  with  the  plasmodium  upon  it  is  to  be 
placed  at  the  foot  of  the  slide,  the  whole  covered  with  a  bell-jar 
and  a  dark  cover  of  pasteboard,  and  from   time  to  time  the 
water  in  the  tumbler  replenished.    In  the  course  of  ten  or  twelve 
hours  some  of  the  protoplasmic  mass  will  climb  up  the  slide  in 
the  form  of  delicate  threads,  which  branch  more  or  less  and  con- 
stitute a  sort  of  network.     The  slide  is  then  transferred  to  the 
stage  of  the  microscope,  care  being  taken  (1)  to  use  onl}-  a 
little  light,  and  (2)  to  avoid  an3'  pressure  by  the  cover-glass. 
The  latter  may  be  prevented  by  fragments  of  glass  placed  under 
the  corners  of  the  cover-glass ;  or,  better  still,  the  cover-glass 
may  be  fastened  on  the  slide  by  means  of  four  minute  drops 
of  cement,  leaving  its  side  exposed,  and  then  the  slide,  thus 
furnished  with  a  cover,  placed  in  the  nearly  vertical  position  al- 
ready advised,  \vhcn  the  plasmodium  will  creep  under  the  (rover, 


CHEMICAL  AND   PHYSICAL  PROPERTIES. 


197 


and  be  all  ready  for  examination,  with  no  disturbance  whatever. 
If  the  plasmodium  is  allowed  to  creep  over  the  face  of  a  slide 
placed  horizontally,  it  is  apt  to  be  too  thick  for  a  demonstration 
of  some  of  the  points  which  are  now  to  be  referred  to. 

541.  Chemical  and  physical  properties  of  protoplasm.     When 
the  plasmodia  of  ^Ethalium  septicutn  collect  in  large  masses  on 
the  surface  of  spent  tan,  they  afford  good  material  for  the  exam- 
ination of  some  of  the  chemical  and  pln-sical  characters  of  pro- 
toplasm ;  but  there  is,  of  course,  the  serious  objection  that  it 
is  impossible  to  obtain  the  protoplasm  in  a  state  of  absolute 
purity.     Upon  such  material,  however,  Reinke  and  Rodewald  x 
have  conducted  some  instructive  experiments,  the  principal  re- 
sults of  which  are  detailed  in  the  following  paragraphs. 

542.  The  organic  substance  of  the  protoplasm  of  ^Ethalium 
proved  to  have  the  following  elementary  composition  : 2  — • 


Per  cent,  air-dried 
substance. 

Per  cent,  dry 
substance. 

First    /£ 
analysis.  \% 

38.56 
5.82 
5.63 

40.52 
6.10 
5.91 

Second    I0' 
analysis.  1^' 

38.61 
5.99 
5.39 

40.47 
6.29 
5.65 

In  both  analyses  oxygen  is  a  fourth  constituent. 

1  Studien  iiber  das  Protoplasm*,  Berlin,  1881. 

2  The  composition  of  the  air-dried  substance  is  approximately  as  follows 

Water 4.80 

Pepsin  and  Myosin 1 .00 

Vitellin 5.00 

Plastin 27.40 

Guanin  ^ 

Xanthin  > 01 

Sarkin     ) 

Ammonic  carbonate 10 

Asparagin  and  other  amides 1.00 

Pepton  and  Peptonoid 4.00 

Lecithin       20 

Glycogen 4.73 

jEthalium  sugar 3.00 

Calcic  compounds  of  higher  fatty  acids     ...      5.83 
Calcic  formate  )  ^2 

Calcic  acetate   \ 

Calcic  carbonate .27.70 

Sodic  chloride 10 

Hydropotassic  phosphate  (P04K2H)     .    .    .    .      1.21 
Iron  phosphate  (P04Fe  ?) 07 


198  PROTOPLASM. 

543.  One  hundred   and  seventy-nine  grams  of  fresh  proto- 
plasm of  a  soft  consistence  were  placed  in  closely  woven  linen 
cloth  and  subjected  to  pressure  by  the  hand ;    58  grams  of  a 
turbid  fluid  were  expressed ;  the  mass  was  then  placed  under 
a  pressure  of  4,000  kilograms,  by  which  62  grams  more  were 
forced  out,  leaving  a  drjT  cake  behind.      Thus  66.7  per  cent 
of  the  mass  was  pressed  out.     The  fluid  thus  expressed  has  a 
specific  gravity  of  1.209.     That  this  fluid  is  intimately  incorpo- 
rated with  the  more  solid  portion  of  the  protoplasm,  appears  from 
the  fact  that  it  cannot  be  forced  from  the  protoplasm  by  cen- 
trifugal force  alone.     To  it  the  name  enchylema  has  been  given  ; 
to  the  solid  matter,  the  name  stroma  is  applicable.    The  amount 
of  water  contained  in  fresh  protoplasm  of  ^Ethalium  septicum 
is  approximately  71.6  per  cent. 

The  reaction  of  protoplasm  is  alkaline. 

544.  In  young  cells  the  protoplasm  exhibits  essentially  the 
same  characteristics  as  those  presented  b}'  the  naked  protoplasm 
of  the  Myxomycetes  already  alluded  to.    The  phenomena  in  cells 
can  be  most  satisfactorily  seen  in  thin-walled  plant-hairs.    These 
should  be  transferred  to  a  glass  slide  with  as  little  injury  as  pos- 
sible, covered  immediately  with  pure  water,  and  examined  under 
a  cover-glass  which  is  prevented  by  bits  of  wax  or  thin  glass 
from  pressing  on  the  delicate  object.    The  stamen-hairs  of  Trad- 
escantia  Virginica,  pilosa,  or  zebrina  are  the  best,  for  in  these 
the  cells  are  sufficiently  large  to  be  managed  without  difficulty, 
and  the  walls  are  perfectly  transparent.     The  cells  in  the  thin 
leaves  of  many  water-plants  answer  very  well,  but  they  generally 
contain  so  much  chlorophyll  that  the  protoplasm  is  obscured. 
The  hairs  of  the  flowers  and  of  the  young  leaves  of  plants  of 
the  Gourd  family  and  those  of  the  nettle1  are  also  excellent 
objects  for  the  study  of  protoplasm ;   and  in  general  it  may  be 
said  that  almost  any  plant-hair,  if  it  is  young  enough  and  has  a 
thin  wall,  will  serve  very  well  (see  Fig.  175). 

545.  Protoplasm  in  cells  exists  as   a  nearly  colorless  mass 


Ammonio-magnesic  phosphate 1.44 

Tricalcic  phosphate 91 

Calcic  oxalate 10 

Chlolesterin 1.40 

Fatty  acids  extracted  by  ether 4.00 

Resinous  matter 1.00 

Glycerin,  coloring-matter,  etc 18 

Undetermined  matters 5.00 

Huxley  :  Protoplasm  (Half  Hours  with  Modern  Scientists,  1871). 


MOVEMENTS.  199 

lining  the  walls  and  extending  irregularly  from  side  to  side  in 
slender  threads.  At  some  one  part  the  mass  appears  a  little 
denser  than  at  others,  and  if  the  outline  of  this  firmer  mass  is 
at  all  well  defined  it  is  easily  recognized  as  the  nucleus  (see 
Fig.  2). 

546.  Circulation  of  protoplasm  in  cells.     Under  a  power  of 
300  diameters  the  delicate  threads  of  protoplasm  can  be  clearly 
seen  to  have  imbedded  in  them  minute  granules  which  are  slowly 
moving.      It  happens  sometimes  that  a  slight  warming  is  re- 
quired before  any  motion  is  apparent.    When  the  current  is  fully 
established,  its  different  changes  can  be  watched  for  a  long  time 
without  other  disturbance  of  the  specimen  than  that  resulting 
from  the  addition  of  water  to  replace  that  lost  by  evaporation. 

Two  features  of  the  motion  require  special  notice:  (1)  the 
granules  do  not  pass  from  one  cell  to  the  contiguous  one,  but 
remain  confined  in  one ;  (2)  the  threads  in  which  the  granules 
move  gradually  change  their  shape  and  direction,  growing  wider 
in  one  place  and  becoming  narrower  in  another,  while  at  the 
points  of  contact  with  the  lining  of  the  wall  the  threads  seem  to 
slip  or  glide  very  slowly,  and  accumulations  of  the  protoplasm 
here  and  there  take  place.  The  movement  of  the  granules  from 
place  to  place  in  a  steady  current  is  called  the  circulation  of 
protoplasm  ;  the  sluggish  changes  of  the  threads  as  they  alter- 
nately increase  and  diminish  in  size  resemble  the  amoeboid 
movements  (see  555  and  Fig.  175). 

547.  In  some  examinations  it  is  instructive  to  add  a  very 
little  glycerin  or  sugar  to  the  water  on  the  slide,  in  order  to 
cause  a  slight  contraction  of  the  protoplasm ;    its  whole  mass 
then  appears  as  a  shrunken  sac,  in  the  interior  of  which  the 
circulation  can  be  detected. 

548.  In  a  good  specimen  of  the  stamen-hair  of  Tradescantia 
the  protoplasmic  currents  are  seen  to  course  in  slender  threads 
with   a   considerable   degree   of  regularity.      In   some   of  the 
threads  or  bands  the  currents  go  in  one  direction,  in  others  in 
another  ;  and  it  occasionally  happens,  as  Hofmeister  has  pointed 
out,  that  two  opposite  currents   may  pass  in  a  single  narrow 
channel. 

549.  There   is   more  or   less  accumulation   of   protoplasmic 
matter  in  the  immediate  vicinity  of  the  nucleus,  and  there  are 
generally  some  slight  projections  into  the  interior  of  the  cell. 
The  rate  of  circulation  appears  to  be  greater  at  the  middle  of 
the  threads  than  at  the  sides  or  ends  of  the  cell. 

550.  If  these  movements  in  a  cell  are  compared  with  the 


200  PROTOPLASM. 

movements  exhibited  by  naked  protoplasm,  no  substantial  dif- 
ference can  be  seen  beyond  that  which  depends  upon  the  con- 
finement of  the  mass  in  one  case  within  practically  rigid  walls. 
The  naked  protoplasm  moves  slowly  from  place  to  place,  by 
thrusting  out  an  irregular  projection  which  soon  enlarges,  and 
in  its  turn  gives  out  new  projections,  while  the  mass  behind  is 
slowly  moving  up.  This  movement  is  identical  with  that  observed 
in  the  amoeba.  In  the  substance  of  a  mass  of  naked  proto- 
plasm granules  can  be  seen  to  move  in  varying  channels ;  and 
this  corresponds  strictly  to  the  movement  known  as  the  circu- 
lation. Moreover,  in  the  naked  protoplasm  larger  or  smaller 
vacuoles  (see  120)  are  observed  to  increase  and  diminish  in  size, 
their  limiting  walls  answering  essentially  to  the  threads  before 
described. 

551.  Rotation  of  protoplasm  in  cells.     The  film  of  protoplasm 
in  contact  with  the  cell-wall  does  not  generally  share  in  the 
movement  of  the  softer  part  which  it  encloses,  but  usually  re- 
mains entirety  stationary,  or  else  very  slowly  shifts  its  posi- 
tion on  the  wall.      In  some  cases,  however,  the  whole  mass 
of  protoplasm  slowly  revolves  on  its  own  axis,  carrying  with 
it   all   imbedded   matters.      This   movement  should   be   called 
rotation  ;  but  the  term  is  often  employed  interchangeably  with 
circulation. 

552.  Rate  of  protoplasmic  movements.      In  the  cells  of  the 
shaft  of  any  Chara  which  has  transparent  walls  —  for  instance, 
Nitella  —  the  rapid  movement  can  be  very  clearly  seen  to  be 
confined  to  the  interior  of  the  protoplasm,  the  outer  part  in  which 
chlorophyll-granules  are  imbedded  not  moving  to  any  great  ex- 
tent, if  indeed  at  all.     At  its  interior  the  protoplasm  moves  with 
what  seems  under  the  microscope  to  be  a  very  rapid  rate  ;  it  is, 
however,  absolutely  very  slow ;  being  only  about  one  and  a  half 
millimeters  per  minute,  at  a  temperature  of  15°  C. 

553.  The  rate  differs  considerably  in   different  plants ;  for 
instance,  according  to  several  observers,  the  distance  traversed 
in  one  minute  at  a  temperature  of  15°  C.  is  as  follows :  — 

Name  of  plant.  mm.  Observer. 

Potamogeton  ciispus,  leaf-cell   .     .     .     .009     .     .  .     Hofmeister. 

Ceratophyllum  demersum,  leaf-cell     .     .094    .     .  .     Mohl. 
Tradescantia  Virginica,  stamen-hair   .     .137 

Sagittaria  sagittcefolia 174     .     ...     Mohl. 

Vallisneria  spiralis 225-1.086  .     Mohl. 

Hydrocharis  Morsus-ranse,  root-hair  .     .543 

Nitella  flexilis,  cells  of  the  shaft    .     ,1.500-1.600  .     Nageli. 


AM(EBO1D   MOVEMENT.  201 

In  the  naked  protoplasm  of  Myxomycetes  the  rates  of  move- 
ment of  the  currents  are  much  greater,  as  Hofmeister  shows  by 
the  following  examples  :  — 

mm.  per  minute. 

Didymium  Serpula     ..-..»   ^ 10. 

Physarura  species 5.4 

554.  The  above  rates  are  not  constant  even  in  the  same  speci- 
men ;  after   having  been  uniform  for  a  few  minutes,  the  rate 
may  slowly  diminish  for  a  time,  the  temperature  and  other  con- 
ditions remaining  apparently  unchanged,  and   then   as  slowly 
increase  until  the  maximum  is  again  reached.     Again,  the  rate 
is  subject  to  sudden  changes.     In  general,  however,  it  is  nearly 
the  same  for  the  same  part  of  a  given  plant. 

555.  The  amoeboid  movement  in  naked  protoplasm  is  rather 
more  sluggish  than  the  circulation,  as  the  following  figures  from 
Hofmeister  show :  — 

mm.  per  minute. 

Didymium  Serpula 0.4 

Physarum'sp 0.29 

Steruonitis  fusca 0.15 

The  far  more  rapid  movement  of  ciliated  protoplasmic  bodies 
will  be  described  under  "Movements." 

556.  The  effects  upon  protoplasm  of  various  agents  —  for  in- 
stance, heat,  light,  electricity,  etc.  — can  be  studied  in  the  same 
cells  in  which  the  movements  are  observed ;  in  fact,  their  effects 
upon  the  movements  themselves  are  among  the  most  striking 
phenomena  noticed.     It  must  be  remembered,  however,  that  in 
experimenting  upon  the  protoplasm  in  cells  which  are  furnished 
with  a  cell-wall  and  provided  with  cell-sap,  other  factors  are 
present  than  those  which  must  be  taken  into  account  in  deal- 
ing with  the  naked  protoplasm  of  plasmodia.     And  hence  it  is 
proper  in  most  cases,  in  interpreting  the  results  obtained  in 
experiments  upon  the  protoplasm  of  cells,  to  speak  of  the  effects 
of  the  agents  upon  thq  cells  themselves. 

557.  Relations  of  protoplasm  to  heat.     In  experimenting  upon 
the  effect  of  heat  on  protoplasm,  the  apparatus  generally  em- 
ployed is  the  so-called  warm  chamber.     In  its  simplest  form  this 
consists  of  a  hollow- walled  box,  having  a  slit  in  which  a  slide 
can  be  placed,  and  at  the  centre  of  the  upper  and  lower  walls 
holes  of  the  same  size  as  the  largest  diaphragm  of  the  micro- 
scope,  so  as  to  allow  light  to  pass  from  the  mirror  directly 
through  the  slide  and  thence  to  the  objective.     Connected  with 
the  box  are  two  tubes  to  which  pieces  of  rubber  tubing  ma}' 


202 


PROTOPLASM. 


be  attached  ;  these  pieces  run  to  a  small  reservoir  of  water  which 
can  be  heated  at  pleasure  by  means  of  a  spirit-lamp,  as  shown 
in  the  figure.  Suppose  a  slide  to  have  upon  it  a  good  specimen 
of  a  stamen-hair  ol'Tradescantia,  furnished  with  sufficient  water 
and  properly  covered.  It  is  placed  in  the  aperture  f  of  the 
hollow  box,  and  the  rest  of  the  apparatus 
is  then  arranged  as  shown  in  the  cut.  The 
rate  of  circulation  of  the  protoplasm  is  now 
carefully  observed,  and  the  temperature 
shown  by  the  thermometer  t  is  also  noted. 
With  increments  of  heat  from  the  upward 
current  of  water  through  the  tube  and 


through  the  box  the  rate  of  the  protoplasmic  circulation  is  in- 
creased. The  amount  of  heat  applied  can  be  easily  regulated 
by  the  height  of  the  reservoir.  If  it  is  desirable  to  observe  the 
effects  of  cold,  the  reservoir  can  be  placed  in  a  vessel  of  ice  and 
raised  above  the  stage  of  the  microscope,  so  that  a  current  of 
cold  water  can  flow  down  through  the  box. 

558.  Experiments  upon  the  effect  of  heat  can  also  be  con- 
veniently conducted  by  means  of  a  less  expensive  apparatus 
which  consists  of  a  double-walled  box  of  zinc  placed  on  firm 
supports  at  the  height  of  a  few  inches  above  the  table,  and  hirge 


RELATIONS   OF   PROTOPLASM   TO   HEAT.  203 

enough  to  receive  the  body  of  the  microscope.  Through  a  hole 
in  the  top  of  the  box  the  tube  of  the  microscope  projects  for  a 
short  distance,  and  the  front  of  the  box  is  furnished  with  a  glass 
window,  which  affords  enough  light  for  the  mirror.  The  space 
between  the  walls  of  the  box  having  been  filled  with  water,  and 
the  object  placed  on  the  stage  of  the  microscope,  a  lamp  under 
the  box  is  lighted,  and  the  effects  of  the  increase  of  temperature 
noted.  It  is  best  in  this  case  to  have  the  thermometer  in  the 
closest  proximity  to  the  slide.  It  is  essential  in  the  use  of  both 
these  instruments  to  note  the  temperature  at  short  intervals, 
and  it  is  only  by  the  greatest  care  in  the  use  of  the  thermometer 
that  any  trustwortlvy  results  can  be  obtained  (see  Fig.  170). 

559.  As  might  be  expected  from  the  nature  of  heat  as  a  mode 
of  molecular   motion,   the   rate   of  protoplasmic   movement   is 
accelerated  by  increase  of  temperature  up  to  a  given  point  (the 
optimum) ;  with  increase  beyond  this  point  the  movement  ma}' 
continue,  but  with  diminished  rapidit}-,  until  an  upper  limit  of 
temperature  (the  maximum)  is  reached,  above  which  no  move- 
ment is  observable.    At  or  very  near  this  limit  structural  changes 
take  place,  and  death  of  the  protoplasm  speedily  ensues. 

560.  The  optimum  temperature  for  protoplasmic  movement 
is  different  for  different  plants,  but  is  not  far  from  37°. 5  C. 

Name  of  plant.                          Optimum  temperature.  Observer. 

Nitella  syncarpa 37°        Nageli.i 

Chara  fcetida 38°.  1 Velten.8 

Vallisneria  spiralis 38°.  75 "     2 

"        40°        Sachs.* 

Anacharis  Canadensis   ....     36°. 25 Velten.2 

561.  The  maximum  temperature  beyond  which  no  movement 
is  seen,  is  also  different  for  different  plants,  but  may  be  given  as 
not  higher  than  50°  C. 

Name  of  plant.                                  Maximum.  Observer. 

Chara  foetida 42°. 81 Velten.2 

Vallisneria  spiralis 45°       "     a 

"        50°        Sachs.* 

Sachs  *  states  that  when  the  hairs  of  Cucurbita  Pepo  are  im- 
mersed in  water  of  46°  or  47°  C.  the  protoplasmic  movements 
are  arrested  within  two  minutes ;  but  that  the  hairs  can  bear 

1  Beitrage  z.  wiss.  Botanik,  1860,  ii.  p.  77. 

2  Flora,  1876,  p.  177  et  seq. 
•  Flora,  1864,  p.  5  et  seq. 

«  Lehrbuch  der  Botanik,  1874,  p.  700. 


204  PROTOPLASM. 

exposure  for  ten  minutes  to  a  temperature  of  49° -50°  in  the  air 
before  arrest  of  movement  takes  place.  In  Tradescantia  hairs 
the  current  stops  within  three  minutes  upon  exposure  in  air  of 
a  temperature  of  49°,  beginning  again  when  the  temperature 
falls. 

562.  The  lower  limit  (minimum)    of  temperature  at  which 
motion  takes  place  may  be  stated  at  0°  C.,  although  — 2°  has 
been  observed  l  in  a  single  plant,  —  Nitella  syncarpa. 

Until  a  temperature  of  at  least  15°  C.  is  attained,  the  move- 
ment is  sluggish. 

563.  Sudden  changes  of  temperature  have  been  said  by  some 
writers  to  cause  a  temporary  arrest  of  the  protoplasmic  move- 
ment.   Thus  de  Vries 2  observed  that  in  the  root-hairs  of  Hydro- 
charis  Morsus-ranse  the  protoplasmic  current  at  21°. 7  C.  was  so 
rapid  that  it  passed  through  one  millimeter  in  205  seconds  ;  but 
upon  sudden  elevation  of  temperature  to  33°  C.,  240  seconds 
were  required  for  it  to  traverse  the  same  distance.     And  Hof- 
meister8  found  that  the  rapid  movement  in  Nitella  flexilis  was 
arrested  in  two  minutes  when  the  specimen  was  taken  from  a 
room  at  18°.5  to  one  at  5°.     But,  on  the  other  hand,  Velten  * 
failed  to  detect  such  an  effect. 

564.  At  or  near  the  maximum  temperature  remarkable  changes 
take  place  in  the  form  of  the  protoplasmic  threads  and  films. 
They  become  more  or  less  rounded,  although  very  irregularly, 
and  may  be  completely  disintegrated.     Such  changes  have  been 
noted  by  Max  Schultze6  at  a  temperature  of  about  40°  C.  in 
the  hairs  of  Urtica,  the  stamen-hairs  of  Tradescantia,  and  the 
leaf-cells  of  Vallisneria.     According  to  Kiihne,6  such  changes 
take  place  within  two  minutes  in  the  plasmodium  of  JEthalium 
septicum  (see  540)  at  a  temperature  of  39°  C. ;  the  plasmodium 
of  Did3rmium  serpula  was  affected  in  the  same  way  at  a  con- 
siderably lower  point,  namely,  30°  C. 

565.  When  subjected  to  a  temperature  lower  than  the  mini- 
mum for  movement,  the  protoplasmic  mass  may  become  disin- 
tegrated, the  solid  part  separating  from  a  watery  portion,  which 
latter  may  freeze.7     If,  now,  very  gradual  increments  of  heat 

Botan.  Zeitung,  1871,  p.  723  (Cohn). 

Archiv.  Neerlandaises,  v.,  1870,  p.  385. 

Die  Lehre  von  der  Pflanzenzelle,  1867,  p.  53. 

Flora,  1876,  p.  213. 

Das  Protoplasma  d.  Rhizopoden  und  Pflanzenzellen,  1863,  p.  48. 

Untersnchungen  iiber  das  Protoplasma,  1864,  p.  87. 

Untersuchungen  Uber  das  Protoplasma,  1864,  p.  101. 


RELATIONS    OF   PKOTOPLASM   TO    HEAT.  205 

are  applied,  the  disorganized  parts  may  become  reunited,  and 
after  a  while  the  movement  may  begin  again.  No  such  recovery, 
however,  is  possible  when  the  protoplasmic  mass  has  become 
disintegrated  by  a  high  temperature  ;  the  change  thus  produced 
is  practically  coagulation.1 

566.  The  temperature  of  certain  hot  springs  in  which  living 
algae  have  been  found  shows  that  protoplasm  can  bear  without 
injury  a  greater  degree  of  heat  than  is  indicated  by  the  figures 
in  561.      Thus  algae  have  been  seen  in  the  following  thermal 
waters :  — 

Temperature.  Observer. 

Carlsbad 53°.  7  C Cohn.2 

Lip  Islands  ....     53°.          ....  Hoppe-Seyler.8 

Dax 57° Serres.* 

California  Geysers  .     .     93°          ....  Brewer.5 

Hoppe-Seyler  found  algae  growing  on  the  edge  of  a  fumarole 
where  they  were  subjected  to  a  temperature  (from  the  escaping 
vapor)  of  60°. 6 

567.  That  the  protoplasm  of  many  kinds  of  seeds  and  spores 
can  preserve  its  vitality  during  exposure  to  dry  air  at  a  tem- 
perature above  that  of  boiling  water  has  been  shown  by  many 
experimenters ; 7  but  unless  the  precaution  is  taken  to  remove 
all  water  from  the  seeds  by  very  careful  and  slow  drying,  any 
temperature  above  100°  C.  is  injurious.     Seeds  thus  cautiously 
freed  from  moisture  have  been  heated  to  110°,  and  even  for  a 
short  time  to  120°,  without  losing  their  power  of  germination 
(see  also  "Germination").     Nor  does  there  seem  to  be  any  es- 
sential difference  between  the  seeds  which  contain  oils  and  those 
which  contain  starch  in  their  capacity  to  endure  high  tempera- 
tures.    Hoffmann8  and  Pasteur9  have  shown  that  the  vitality  of 
perfectly  dry  seeds  and  spores  mav  in  some  cases  be  retained 
until  a  temperature  of  130°  C.  is  reached. 

i  Pfefier  :  Pflanzenphysiologie,  1881,  ii.  p.  386.  2  Flora,  1862,  p.  538. 

8  Pfliiger's  Archiv.,  1875,  p.  118.  4  Botan.  Centralblatt,  1880.  p.  257. 

6  Am.  Journ.  Sc.  and  Arts,  2d  series,  xli.  391. 

6  Pfliiger's  Archiv.,  1875,  p.  118. 

A  much  higher  temperature  is  noted  by  Humboldt ;  namely,  85°  C.  for  the 
hot  spring  of  Trinchera,  Caraccas,  in  which  he  found  the  roots  of  certain  plants 
growing. 

7  Milne  Edwards  and  Colin  :  Ann.  desSc.  nat.,  ser.  2,  tome  i.,  1834,  p.  264; 
Sachs's  Handbuch  der  Experimental- Physiologic,  1865,  p.  65  et  seq.  ;  Just,  in 
Cohn's  Beitrage  zur  Biologie  der  Pflanzen,  1877,  p.  311. 

8  Pringsheim's  Jahrb.,  1860,  p.  324. 

9  Ann.  d.  Chimie  et  de  Physique,  1862,  p.  90. 


206  PROTOPLASM. 

568.  On  the  other  hand,  the  protoplasm  of  dry  seeds  can  be 
subjected  to  extremely  low  temperatures  without  suffering  any 
injury  (see  "Germination"). 

569.  The  relations  of  protoplasm  to  light  are  best  examined  in 
the  plasmodia  of  the  myxomycetes  and  the  hairs  of  Tradescantia, 
for  here  they  are  not  complicated  by  the  presence  of  chlorophyll 
(which,  as  will  be  seen  later,  exerts  a  marked  influence).     Ac- 
cording to  Hofmeister,  plasmodia  thrust  forth  longer  and  more 
numerous  processes  in  darkness  than  in  light.     In  ^Ethalium  sep- 
ticum  the  processes  developed  in  light  are  short  and  compressed, 
while  those   grown   in  darkness   are  long,  slender,  and  thin.1 
This  is  especially  noticeable  when  the  light  falls  only  on  one 
side   of  the  mass.     In  some  of  Baranetzky's  experiments,2  in 
which  the  incident  rays  of  light  were  parallel  to  the  substratum 
(wet  filtering-paper)  on  which  the  plasmodium  was  placed,  the 
change   of  form    resulting   from    diminished  extension    on    the 
lighted  side  and   increased   extension  on   the  other  was  very 
marked  after  fifteen  minutes'  exposure  to  bright  sunlight,  while 
in  diffused  light  half  an  hour  was  required  for  a  similar  change. 
These   results   should    be    compared    with    those    obtained    by 
Schleicher,8  who  observed  that  young  plasmodia  move  towards 
light  of  low  intensity,  and  that  older  plasmodia  ma}*  move  even 
towards  strong  light.     The  movement  into  bright  light  appears 
to  just  precede  the  formation  of  the  spores. 

570.  The  more  refrangible  rays  of  light  —  that  is,  the  violet 
and  indigo  —  appear  to  be  more  efficient  in  influencing  move- 
ment than  are  the  less  refrangible,  — the  red  and  yellow. 

571.  The  "  circulation"  of  protoplasm  in  plant-hairs  goes  on 
not  only  in  darkness,  but  even  when  the  hairs  are  developed  on 
plants  blanched  by  absence  of  light.4     No  marked  effect  upon 
the  rate  of  such  movement  appears  to  be  caused  by  presence  or 
absence  of  light,  except  so  far  as  the  concomitant  action  of  heat 
comes  into  play.    Hofmeister  states  that  he  saw  the  protoplasmic 

1  Die  Lehre  von  der  Pflanzenzelle,  1867,  p.  21. 

2  Memoires  de  la  soc.  des  sciences  nat.  de  Cherbourg,  1875,  p.  340.     It  is, 
however,   well  known  that  plasmodia  often  emerge  slowly  from  their  sub- 
stratum ;  for  instance,  tan,  if  the  surface  is  only  very  faintly  lighted. 

8  Jenaische  Zeitschrift,  1878,  p.  620. 

*  Sachs  :  Botan.  Zeit.,  1863,  Supplement.  Reinke  :  ibid.,  1871,  p.  797. 
Kraus  :  ibid.,  1876,  p.  504.  Few  observations  have  been  recorded  upon  the 
effect  upon  protoplasmic  movements  of  sudden  changes  of  illumination.  In 
the  case  of  an  amoeba  (Pelomyxa  palustris)  Engehnann  found  that  light, 
and  not  its  sudden  withdrawal,  appeared  to  exert  a  stimulant  effect  (Pfeffer  : 
Pflanzenphysiologie,  ii.  p.  387). 


RELATIONS   OF   PROTOPLASM   TO    ELECTRICITY.       207 

movement  as  distinctly  in  hairs  which  had  been  developed  in 
darkness,  and  had  remained  without  light  for  thirty  hours,  as  in 
any  which  had  grown  in  the  open  daylight.  According  to  Du- 
trochet,  it  requires  a  withdrawal  of  the  light  for  about  twenty 
days  to  cause  an  entire  cessation  of  the  movement  in  Chara. 

The  effect  of  very  intense  light,  and  the  influence  exerted  by 
it  upon  protoplasm  containing  chlorophyll,  will  be  examined 
under  "  Assimilation." 

572.  Relations  of  protoplasm  to  electricity.     Chemical  changes 
within  the  plant  result  in  the  production  of  electrical  currents  in 
protoplasm ;    at  this  point  it  is  proper  to  examine  briefly  the 
effect   produced   upon   protoplasm    by   continued   and   induced 
currents. 

When  the  plasmodium  of  a  myxomycete  is  placed  between 
platinum  electrodes  on  a  glass  slide  under  the  microscope,  and 
a  current  sent  through  the  mass  from  one  small  Grove  element, 
very  little  if  any  effect  is  observable ;  but  if  the  current  from  a 
few  elements  is  employed,  there  is  at  once  more  or  less  rounding 
of  the  branched  mass,  and  there  may  also  be  a  reversal  of  the 
course  of  the  circulation.  When  more  elements  are  used,  the 
protoplasm  may  be  killed.  If  the  protoplasm  in  cells  be  experi- 
mented upon,  nearly  similar  phenomena  are  noticed.  Protoplasm 
is  not  a  good  conductor  of  electricity.  JUrgenseu  made  some 
experiments  on  the  action  of  a  current  from  small  Grove  ele- 
ments upon  the  leaf-cells  of  Vallisneria  spiralis.  A  continued 
current  from  one  element  did  not  cause  any  appi'eciable  change 
in  the  protoplasmic  movement ;  but  when  two,  three,  or  four 
were  employed,  the  current  retarded  the  movement,  and  after 
a  while  completely  arrested  it.  In  those  cases  where  the  move- 
ment had  been  simply  checked,  it  was  re-established  in  full  in- 
tensity shortly  after  cutting  oh"  the  current  of  electricity  ;  but  in 
those  where  it  had  been  entirely  stopped,  it  did  not  begin  again. 

573.  The  effect  of  an   interrupted  current  of  electricity  is 
essentially  the  same  as  that  produced   by  mechanical  shock. 
The  protoplasm  generally  contracts  at  certain  points  forming 
small  roundish  masses  in  the  lines  of  the  slender  threads,  and 
the  movements  are  arrested. 

574.  Hofmeister  states  that  a  constant  current  is  practically 
without  any  influence  upon  the  circulatory  movement  in  the  cells 
of  Chara,   but   that  the  interruption  of  the  current   produces 
nearly  the  same  effect  as  a  sudden  mechanical  shock  or  a  sharp 
change  of  temperature.     He  observed  essentially  the  same  phe- 
nomena in  the  hairs  of  the  nettle,  although  in  these  there  was 


208  PROTOPLASM. 

also  more  or  less  of  the  aggregation  into  rounded  masses  alluded 
to  in  564. 

575.  The  effect  of  mechanical   irritation  upon  protoplasm  in 
plants  can  be  easily  examined  in  cells  or  in  plasmodia.     When 
a  cell  of  Nitella  which  exhibits  rapid  circulation  of  protoplasm 
is  held  somewhat  firmly  by  pressure  on  the  cover-glass,   the 
movement  is  arrested  instantly,   but  after  a  short  time  it  is 
resumed.      Even  in  those  cases  where   the  pressure  has  been 
sufficient  to  disturb  the  arrangement  of  the  chlorophyll  granules, 
the  arrested  motions  are  soon  to  be  seen  again.     For  experi- 
ments upon  the  effect  of  pressure  and  shock,  the  stamen-hairs  of 
Tradescantia  are  even  better  than  cells   of  Nitella   or   Chara, 
for  pressure   brings   about   an  apparent   disintegration  of  the 
threads,  and  all  motion  is  suspended  for  several  minutes  ;  but  if 
the  injury  has  not  been  too  severe,  it  soon  begins  again.     How 
far  such  injuries  can  be  carried  without  affecting  the  vitality  of 
the  protoplasm,  may  be  seen  from  the  following  observations. 

According  to  Gozzi,1  if  a  cell  of  Chara  is  ligated  firmly,  the 
circulation  is  checked  for  a  short  time,  and  then  begins  in  each 
half  of  the  cell.  It  is  stated  by  Hofmeister  that  when  a  root- 
hair  of  Hydrocharis  Morsus-ranae  is  severed,  the  protoplasm  in 
the  cell  remains  motionless  for  a  short  time,  during  which  the 
cut  surface  of  the  cell  is  being  closed  by  a  portion  of  the  proto- 
plasmic mass.  When  the  surface  is  completely  closed,  the  cir- 
culation begins  again  within  the  healed  cell. 

576.  Rosanoff  s  observation,2  which  has  been  repeated  many 
times,    is  of  much   interest   in   connection   with  this   subject. 
When  a  cell  from  the  endosperm  of  Ceratophyllum  demersum, 
having  rapid  circulation  of  protoplasm,  is  placed  under  the  mi- 
croscope, and  a  slight  pressure  is  exerted  on  the  cover-glass 
for  a  moment,  the  circulation   stops  at  once,  the  thick  axile 
threads  of  protoplasm  begin  to  round  at  one  or  more  places,  and 
from  the  aggregations  slight   processes,  somewhat  like  tenta- 
cles, appear.     After  a  while  these  are  retracted,  and  the  normal 
circulation  is  resumed.      But  sometimes  it  happens  that  these 
tentacles  become  separated  from  the  threads  to  which  they  be- 
long, for  a  time   lie  without  movement  near  them,   and  then 
become  again  confluent  with  them. 

Mechanical  shock 8  causes  the  active  plasmodia  of  the  myxo- 

1  Quoted  by  Hofmeister  in  Die  Lehre  von  der  Pflanzenzelle,  1867,  p.  50. 

2  Die  Lehre  von  der  Pflanzenzelle,  p.  51. 
8  Hofmeister  :  Pflanzenzelle,  p.  26. 


RELATIONS   OF   PROTOPLASM  TO   GRAVITATION.       209 

im'cetes  to  become  rounded  into  the  form  of  somewhat  flattened 
drops,  from  which  slender  branches  protrude  after  a  short  time. 
If  pressure  is  now  made  upon  those  portions  of  the  branched 
plasmodium  in  which  circulation  is  to  be  seen,  the  movement 
stops  at  once,  and  is  not  resumed  for  two  or  three  minutes ; 
but  after  that  period  of  rest  it  goes  on  as  before.  When  a 
plasmodium  is  cut  in  halves,  the  circulation  is  to  be  seen  after 
a  while  in  the  separated  portions.1 

577.  Relations  of  protoplasm  to  gravitation.     Concerning  the 
influence  of  gravitation  on  the  form  assumed  by  protoplasm,  it 
need  only  be  said  here  that  the  less  dense  plasmodia  appear  some- 
times to  yield  to  this  force.    But  Ffeft'er 2  found  that  in  a  saturated 
atmosphere  the  plasmodium  of  jEthalium  moved  in  the  dark  with 
equal  freedom  whether  the  moist  bibulous  paper  on  which  it  rested 
was  held  horizontally  or  vertically  ;   Strasburger 8  also  has  noted 
the  same  fact.     If  one  part  of  the  paper  is  more  moist  than  an- 
other, it  is  to  the  very  wet  spot  that  the  plasmodium  wanders. 

578.  Relations  of  protoplasm  to  moisture.     The  relations  of 
water  to  the  activity  of  protoplasm  are  not  yet  thoroughly  under- 
stood.    It  has  been  seen  (577)  that  there  is  a  tendency  of  plas- 
modia to  move  to  the  points  where  there  is  the  most  moisture  ; 
and  in  general  it  may  be  said  that  a  large  amount  of  water  is 
favorable   to  all  protoplasmic  movements.      Thus   Dehnecke  * 
found  that  the  protoplasm  in  the  cells  of  the  collenchyma  of 
Balsamina  exhibited  no  circulation  until  the  section  had  been 
placed  in  water ;  and  the  same  phenomena  can  be  shown  in 
sections  of  many  active  plants. 

On  the  other  hand,  Velten  has  shown  that  in  some  cases  the 
protoplasmic  movement  stops  when  a  plant-hair  is  placed  or  kept 
for  a  time  in  water,  but  is  resumed  if  it  is  transferred  to  a  dilute 
solution  of  gum-arabic,  although  the  protoplasm  was  furnished 
with  a  greater  supply  of  water  in  the  former  than  in  the  latter 
case. 

579.  Some  harmless  plasmolytic  agents  (see  p.  27),  for  in- 
stance a  dilute  solution  of  sugar,  added  to  the  water  in  which  the 

1  Pfeffer  :  Pflanzenphysiologie,  ii.  390. 

2  Pfeffer :  Pflanzenphysiologie,  ii.  388. 

8  Wirkung  des  Lichtes  auf  Schwarmsporen,  1878,  p.  71.  Dehnecke  (Ueber 
nicht  assimilirende  Chlorophyllkorper,  1880)  has  shown  that  the  various 
bodies  which  occur  in  protoplasm  of  cells  —  for  instance,  chlorophyll  granules, 
starch-grains,  and  the  like  —  have  a  marked  tendency  to  sink  to  that  part  of 
the  cellulose  wall  which  is  lowest.  The  change  of  position  takes  place  some- 
times in  a  few  minutes,  sometimes  only  after  several  hours. 

4  Flora,  1881,  p.  8. 

14 


210  PROTOPLASM. 

protoplasm  of  the  cells  of  Tradescantia  stamen-hairs  is  exhibit- 
ing rapid  circulation,  cause  an  increase  in  the  rate  of  movement. 
This  fact  has  been  considered  to  show,  in  connection  with  the 
cases  mentioned,  that  for  the  most  rapid  circulation  of  proto- 
plasm there  must  be  a  definite  amount  of  water, — the  optimum. 

580.  When  any  of  these  plasmolytic  agents  are  used  in  too 
concentrated  a  solution  they  may  exert  a  much  more  marked 
effect  upon  the  protoplasmic  contents  of  a  cell ;  not  only  does 
all  movement  cease,  but  the  mass  shrinks  into  small  bulk,  and 
does  not  afterwards  recover  its  former  shape  and  size.     As  a 
result  of  their  action,  two  other  phenomena  are  presented :  (1)  the 
protoplasm  of  one  cell  can  be  seen  in  some  cases  to  be  connected 
through  the  cell-wall  with  the  protoplasm  in  the  adjoining  cell ; 
(2)  a  change  takes  place  in  the  firmness  or  turgor  of  the  cell- 
wall.    Both  of  these  phenomena  must  receive  attention  at  a  later 
stage.     When  a  cell  containing  living  protoplasm  is  placed  in  a 
harmless  and  dilute  solution  of  any  coloring-matter,  for  instance 
logwood,  its  wall  becomes  more  or  less  tinged  by  the  dye,  but 
the  protoplasm  retains  for  a  while  at  least  its  power  of  move- 
ment, and  does  not  take  up  any  of  the  dye.     If,  however,  the 
protoplasmic  mass  is  injured  or  dead,  it  absorbs  the  coloring- 
matter  with  great  avidity. 

581.  Relations  of  protoplasm  to  various  gases.     Experiments 
upon  the  effects  of  gases  on  the  behavior  of  protoplasm  can 
be  best  conducted  by  means  of  the  simple  gas-chamber  shown 
in  Fig.  195.     A  current  of  the  gas  employed  is  drawn  through 
the  tube  a  by  means  of  any  simple  aspirator;    and  in  a  few 
seconds  the  specimen  previously  placed  upon  the  glass  at  b, 
and  protected  by  a  cover-glass,  is  thoroughly  surrounded  by 
it.      By  the  use  of  this  apparatus  it  has  been  found  that  the 
presence  of  free  oxygen  is  essential  to  protoplasmic  movements. 
Hofmeister  and  Kiihne  have  shown  that  when  this  gas  is  no 
longer  supplied  to   the   protoplasmic  mass  or  to  the  cells  in 
which  the  protoplasm  is  contained,  all  movements  cease.     Thus 
Hofmeister1  found  that  the  circulation  of  Nitella  was  completely 
arrested  in  thirteen  minutes  after  the  air  was  wholly  removed. 
Kiihne2  replaced  by  hydrogen  the  air  in  which   the   hairs   of 
Tradescantia  had   shown   rapid   movement,   and   after   several 
hours  all  motion  was  arrested. 

582.  Corti,8  the  discoverer  of  the  circulation  in  Nitella,  placed 

1  Die  Lehre  von  der  Pflanzenzelle,  p.  49. 

2  Untersuchungen  iiber  das  Protoplasma,  1864,  p.  107. 
8  Meyen  :  Pflanzenphysiologie,  ii.  224. 


STRUCTURE   OF   PROTOPLASM.  211 

cells  in  which  the  movements  were  plainly  seen,  in  olive-oil,  in 
order  to  exclude  the  air.  A  short  time  after  this  was  done  the 
movement  stopped.  In  Hofmeister's l  repetition  of  Corti's  ex- 
periment the  arrest  of  the  protoplasmic  movement  occurred  in 
five  minutes  in  olive-oil ;  after  the  oil  had  been  carefully  poured 
off,  the  movements  recommenced  in  thirty  minutes. 

583.  Kiihne  experimented  also  upon  the  replacement  of  the 
oxygen  needful  for  protoplasmic  movements  by  carbonic  acid, 
and   found   this   gas   much   better  than  oil  for  excluding  air. 
Upon  removal  of  the  plant-hairs  from  oil,  it  is  difficult  to  take 
away  the  last  trace  of  adherent  oil. 

584.  The  ordinary  anaesthetics,  chloroform  and  ether,  arrest 
the  movements  of  protoplasm.2 

585.  The  structure  of  protoplasm.     Having   thus   briefh"  ex- 
amined- some  of  the  more  striking  phenomena  of  protoplasmic 
movement,  the  question  must  now  be  asked,  What  is  the  struc- 
ture of  a  substance  which  exhibits  these  phenomena? 

By  the  highest  power  of  the  microscope  it  appears  as  a  homo- 
geneous hyaline  mass  holding  in  its  substance,  but  apparently 
as  foreign  bodies,  very  minute  granules.  But  when  the  proto- 
plasmic matter  is  stained  1>3T  the  skilful  use  of  pigments,  its 
homogeneous  character  disappears. 

586.  Schmitz  has  confirmed  and  extended  the  observations 
of  Frommann,  which  show  that  in  some  cases  at  least  the  pro- 
toplasmic body  is  a  reticulated  framework  of  extremely  delicate 
fibrils,  between  the  meshes  of  which  is  a  homogeneous  liquid. 
There   is   unobstructed   communication    between    the    different 
meshes,   so  that  the  whole  of  the  liquid  may  be  regarded  as 
practically  one  mass.     The  network  of  fibrils  does  not  possess 
any  rigidity,   but  is  constantly  mobile  under  favorable  condi- 
tions, and  undergoes  manifold  changes  of  form.    The  reticulated 
structure  is  most  clearly  seen  in  the  parietal  protoplasm,  and  the 
larger  bands  of  cells  which  contain  relatively  considerable  sap. 

,  When,  after  hardening,  protoplasm  is  carefully  stained  with 
haematoxylin,  the  whole  mass  appears  to  be  equally  and  evenly 
colored  ;  but  it  is  in  realit}-  only  the  network  which  takes  up  the 
color,  the  liquid  in  the  meshes  remaining  uncolored. 

Imbedded  in  the  protoplasm,  especially  in  the  inner  portions, 
there  are  generally  minute  granules  which  have  a  high  degree 
of  refringency,  and  which  stain  very  deeply  with  the  dye;  these 
are  the  microsomata  of  Hanstein. 

1  Die  Lehre  von  der  Pflanzenzelle,  p.  49. 

2  Claude  Bernard  :  Lemons  sur  les  Phenomeues  tie  la  Vit>,  1879. 


212  PROTOPLASM. 

587.  Up  to  the  present  time  the  microscope  has  not  revealed 
more  than  these  facts  respecting  the  intimate  structure  of  proto- 
plasm, and  from  these  alone  no  clear  conception  can  be  formed 
of  the  mechanics x  of  protoplasmic  movements. 

588.  It  is  just  at  this  stage  of  the  inquiry  respecting  the 
structure  of  protoplasm   that   many  have  sought  to  apply  an 
hypothesis    known    as    Nageli's ;    namel}-,    that   all   organized 
bodies  consist  of  structural  particles  (termed  micellae) ,  each  of 
which  is  individually  enveloped  by  a  film  of  water  holding  vari- 
ous substances  in  solution.    According  to  Nageli's  view,  as  origi- 
nally given,  the  micellae  are  never  spherical,  but  possess  a  true 
crystalline  character,  as  shown  by  the  relations  of  organized 
bodies  to  polarized  light.2    These  micellae  are  believed  to  obey 

1  Hofmeister  regarded  protoplasmic  movements  as  directly  dependent  upon 
changes  in  the  capacity  of  living  protoplasm  for  absorbing  water,  shown  by 
pulsating  vacuoles  (see  120).     In  the  mass  of  a  plasmodium,  or  in  the  free 
spores  of  some  algae,  there  are  generally  to  be  detected  easily  under  the  micro- 
scope minute  spherical  cavities  tilled  with  watery  sap  which  are  constantly 
changing  in  size.    Their  rhythm  of  change,  or  pulsation,  as  it  is  called,  is  differ- 
ent for  different  plants,  varying  from  a  few  seconds  to  as  many  hours.     Their 
increase  in  size  is  usually  gradual  until  the  maximum  is  reached,  when  sud- 
denly the  cavity  or  vacuole  contracts  even  to  the  point  of  vanishing,  and 
then  it  slowly  begins  to  form  again  at  the  same  place  in  the  mass.     The 
rhythm  of  the  pulsations  can  be  made  to  vary  with  changes  in  the  surround- 
ings ;  for  instance,  with  changes  of  temperature,  or  by  the  application  of  dilute 
solutions,  or  by  any  agent  which  modifies  the  absorptive  power  of  proto- 
plasm for  water.     But  these  agents  aVe  also  efficient  in  controlling  the  rate 
of  protoplasmic  movement.     The  spontaneously  pulsating  vacuoles  appear  to 
indicate  that  the  absorptive  power  of  protoplasm  changes  spontaneously,  and 
is  different  successively  in  different  parts  of  the  mass,    thus  disturbing  the 
equilibrium  of  the  soft  mass  sufficiently  to  force  some  portions  from  place 
to  place.     But  Hofmeister  gave  no  explanation  of  the  cause  of  variations  in 
the  imbibition  power  of  protoplasm. 

2  In  his  earliest  work  on  the  subject  (Die  Starkekorner,  1858)  Nageli  applied 
the  word  molecule  (which  had  not  then  obtained  such  general  acceptance  in 
chemistry  and  physics,  with  a  different  signification)  to  what  he  now  calls  the 
micella.     His  hypothesis  has  undergone  sundry  changes  from  time  to  time, 
one  of  his  last  important  publications  (Theorie  der  Garung,  1879)  containing 
some  modifications. 

The  terminology  now  proposed  by  Nageli  applies  the  word  pleon  to  those 
aggregates  of  molecules  which  cannot  be  increased  or  diminished  without 
changing  their  chemical  nature  ;  for  instance,  crystals  which  contain  water  of 
crystallization  would  be  called  pleons,  for  the  molecule  H20  has  a  definite 
numerical  relation  to  the  molecules  of  the  salts,  and  examples  of  similar  pleons 
are  afforded  by  such  compound  salts  as  the  alums. 

Compare  with  this  the  following  statement :  — 

"  It  has  also  been  a  question  among  chemists  whether  molecular  combination 
was  possible ;  in  other  words,  whether  it  is  possible  for  molecules  of  different 


HYPOTHESIS.  .  213 

the  following  attractions :  (1)  that  of  cohesion,  by  which  each 
individual  micella  is  an  aggregate  of  molecules ;  (2)  that  which 
tends  to  bring  adjacent  micellae  together ;  (3)  that  of  adhe- 
sion, by  which  the  surfaces  of  the  micellae  retain  their  films  of 
water. 

kinds  to  combine  chemically,  each  preserving  its  integrity  in  the  compound.  .  .  . 
Any  antecedent  improbability  on  theoretical  grounds  is  far  more  than  out- 
weighed by  the  evidence  of  a  large  number  of  compounds  whose  constitution 
is  most  simply  explained  on  the  hypothesis  of  molecular  combination.  For 
example,  in  the  crystalline  salts  it  is  impossible  to  doubt  that  the  water 
exists  as  such,  not  as  a  part  of  the  salt  molecule,  but  combined  with  it  as  a 
whole.  So  also  there  are  a  number  of  double  salts  whose  constitution  is  most 
simply  explained  on  a  similar  hypothesis"  (Cooke's  Chemical  Philosophy, 
1882,  p.  137). 

The  word  micella  is  applied  by  Nageli  to  those  aggregates  of  molecules 
which  (like  crystals)  can  increase  or  diminish  in  size  without  changing  their 
chemical  nature.  The  micella  is  assumed  to  be  much  larger  than  the  pleon. 
"The  internal  structure  of  the  micella  is  crystalline,  while  the  exterior  may 
assume  any  shape. "  The  micellae  unite  to  form  micellar  aggregates  ;  of  such 
the  crystalline  protein  granules  afford  a  good  example.  Thus,  according  to 
Nageli,  five  terms  must  be  recognized,  —  the  atom,  the  molecule,  the  pleon,  the 
micella,  and  the  micellar  aggregate.  Pfeffer  applies  a  general  term,  Tagma,  to 
all  aggregates  of  molecules,  thus  bringing  under  one  head  the  pleon,  micella, 
and  micellar  aggregate  ;  and  he  applies  the  name  Syntagma  to  all  bodies  made 
up  of  tagmata.  The  subject  will  be  again  referred  to  under  "Osmosis." 

To  make  clearer  the  conception  of  a  micella,  it  may  be  well  to  examine 
briefly  two  terms  in  common  use  ;  namely,  atom  and  molecule. 

When  a  solid  body,  for  instance  a  crystal  of  sodic  chloride  (common  salt), 
is  mechanically  separated  into  the  smallest  possible  fragments,  each  particle 
still  possesses  all  the  properties  of  salt.  Beyond  this  mechanical  limit  of  sepa- 
ration the  process  of  subdivision  may  be  carried  still  further  by  solution  : 
the  minutest  fragments  of  the  salt  can  be  broken  up  and  diffused  through  the 
solvent,  and  yet  not  lose  their  essential  character  as  salt ;  in  fact,  they  can  be 
again  recovered  without  change  from  the  solution.  But  it  is  impossible  to  go 
beyond  this  latter  limit  of  separation  without  altering  the  essential  properties 
of  the  substance.  In  other  words,  by  this  subdivision  the  physical  limit  has 
been  reached  ;  namely,  the  molecule. 

A  molecule  is  understood  to  be  the  smallest  amount  of  any  substance 
which  can  exist  as  such  in  the  free  state.  Hence  the  molecule  is  the  physical 
unit. 

If,  however,  the  salt  is  subdivided  by  chemical  means,  —  for  instance,  by  the 
action  of  strong  sulphuric  acid,  —  its  identity  is  destroyed,  and  its  component 
parts  enter  into  new  relations,  and  cannot  be  restored  to  their  original  relations 
except  by  an  exceedingly  complicated  process.  In  other  words,  the  physical 
limit  has  been  overpassed  and  the  chemical  limit  reached  ;  namely,  the  atom. 

Atom  is  generally  defined  as  ' '  the  smallest  amount  of  a  given  substance 
which  can  exist  in  combination,"  or  "the  smallest  mass  of  nn  element  that 
exists  in  any  molecule."  The  atom  is  the  chemical  unit. 

Atoms  are  variously  combined  to  form  molecules  :  molecules  are  variously 
aggregated  to  form  masses. 


214  PROTOPLASM. 

Contiguous  micellae  in  any  organized  substance,  for  instance 
cell-wall  or  starch,  frequently  possess  different  chemical  charac- 
ters, as  is  shown  by  the  fact  that  from  such  a  substance  one  por- 
tion can  be  taken  without  materially  disturbing  the  external  form. 

589.  By  means  of  the  changes  which  go  on  in  the  formation 
of  new  micellae,  and  in  their  reconstruction,  it  is  sought  to  account 
for  the  nutrition,  growth,  and  movements  of  organized  substances. 
This  is  essentially  the  basis  on  which  Engelmann1  founds  his 
explanation  of  the  movements  of  protoplasm.2 

590.  Continuity  of  protoplasm.     It  was  supposed  until  recently 
that  the  protoplasm  in  one  young  cell  is  completely  shut  off  from 
that  in  contiguous  cells  by  an  imperforate  cell-wall,  and  that  even 
in  the  cases  where  the  wall  is  perforate  there  is  no  communi- 
cation  of  protoplasm  through   the  pores.     There  is  abundant 
evidence  to  show  the  incorrectness  of  this  view.     In  some  cases 
the  protoplasm  in  one  cell  is  practically  continuous  with  that  in 

1  Hermann's  Handbuch  der  Physiologic,  i.  1879,  p.  374. 

2  The  application  of  this  hypothesis  by  Sachs  is  given  somewhat  fully  in 
the  following  extract  (Text-book   of  Botany,   2d   Eng.   ed.,    1882,  p.  666)  : 
"Chemical  compounds  of  the  most  various  kinds  meet  between  the  micellae 
of  an  organized  body,  so  that  they  act  upon  and  decompose  one  another.     It 
is  certain  that  all  growth  continues  only  so  long  as  the  growing  parts  of  the 
cell  are  exposed  to  atmospheric  air ;  the  oxygen  of  the  air  has  an  oxidizing 
effect  on  the  chemical  compounds  contained  in  the  organized  structure  ;  with 
every  act  of  growth  carbon  dioxide  is  produced  and  evolved.     The  equilibrium 
of  the  chemical  forces  is  also  continually  disturbed  by  the  necessary  production 
of  heat ;  and  this  may  also  be  accompanied  by  electrical  action.     The  move- 
ments of  the  atoms  and  molecules  within  a  growing  organized  body  represent 
a  definite  amount  of  work,  and  the  equivalent  forces  are  set  free  by  chemical 
changes.     The  essence  of  organization  and  life  lies  in  this  :  —  that  organized 
structures  are  capable  of  a  constant  internal  change  ;  and  that,  as  long  as  they 
are  in  contact  with  water  and  with  oxygenated  air,  only  a  portion  of  their  forces 
remains  in  equilibrium  even  in  their  interior,  and  determines  the  form  or  frame- 
work of  the  whole  ;  while  new  forces  are  constantly  being  set  free  by  chemical 
changes  between  and  in  the  molecules,  which  forces  in  their  turn  occasion 
further  changes.    This  depends  essentially  on  the  peculiarity  of  micellar  struc- 
ture, which  permits  dissolved  and  gaseous  (absorbed)  substances  to  penetrate 
from  without  into  every  point  of  the  interior,  and  to  be  again  conveyed  out- 
wards.    Neither  the  chemical  nor  the  molecular  forces  are  ever  in  equilibrium 
in  the  protoplasm  ;  the  most  various  elementary  substances  are  present  in  it  in 
the  most  various  combinations  ;  fresh  impulses  to  the  disturbance  of  the  internal 
equilibrium  are  constantly  being  given  by  the  chemical  action  of  the  oxygen 
of  the  air  ;  and  energy  is  continually  being  set  free  at  the  expense  of  the  proto- 
plasm itself,  which  must  lead  to  the  most  complex  actions  in  a  substance  of  so 
complicated  a  structure.     Every  impulse  from  without,  even  when  impercep- 
tible, must  call  forth  a  complicated  play  of  internal  movements,  of  which  we 
we  able  to  perceive  only  the  ultimate  effect  in  an  external  change  of  form." 


CONTINUITY   OF   PROTOPLASM   IN   CELLS.  215 

the  next,  by  means  of  delicate  threads  which  pass  through 
pores  in  the  intervening  cell-wall.  Doubtful  instances  afforded 
by  the  cribrose-cells  have  been  already  alluded  to  (see  279). 
The  endosperm  cells  of  seeds  of  Staychnos  Nux-vomica  afford 
a  well-marked  example  of  the  cases  of  communication  between 
cells  of  seeds.  Tangl 1  advises  that  very  thin  sections  parallel 
to  the  flat  surface  of  the  seed  be  shaken  with  dilute  tincture 
of  iodine  or  with  a  solution  of  iodine  in  iodide  of  potassium  for 
about  five  minutes,  and  then  thoroughly  washed  with  pure  water. 
The  protoplasmic  and  other  contents  of  the  uninjured  cells  will 
then  appear  as  a  contracted  ball  having  somewhat  the  shape  of 
the  cell.  From  the  mass  in  one  cell  minute  threads  run  through 
pores  or  canals  in  the  wall  to  the  masses  in  the  adjoining  cells, 
and  there  is  no  break  in  their  continuity.  In  the  endosperm  of 
the  allied  species,  Strychnos  potatorum,  Tangl  did  not  detect 
canals  of  the  character  found  in  S.  Nux-vomica. 

Gardiner2  has  demonstrated  the  existence  of  communication 
between  the  protoplasmic  masses  in  contiguous  cells  of  the  pul- 
vini  of  the  leaves  of  some  plants  having  the  power  of  motion. 
When  sections  of  these  leaves  are  placed  in  a  solution  of  a  salt 
which  causes  contraction  of  the  protoplasm,  the  shrunken  mass 
is  seen  to  be  connected  with  the  cell-wall  by  extremely  delicate 
threads  of  protoplasm.  The  threads  can  be  traced  to  pits  in  the 
wall,  and  there  it  can  be  seen  that  they  are  exactly  opposite  the 
threads  on  the  other  side  of  the  wall.  If  the  solution  of  the  salt 
used  is  too  strong,  some  of  the  threads  may  be  ruptured,  and 
then  one  free  end  of  each  thread  will  retract  to  the  main  mass 
while  its  other  part  goes  to  the  cell-wall.  If  fresh  sections  are 
treated  with  strong  picric  acid,  and  then,  after  washing  in  alco- 
hol, are  stained  with  anilin  blue,  the  continuity^  of  the  proto- 
plasm in  uninjured  cells  becomes  apparent.  Mimosa  affords 
excellent  material  for  this  purpose. 

Hillhouse 8  reports  similar  continuity  of  protoplasm  in  the  cortex 
of  the  stem  of  Laburnum,  and  in  the  petiole  of  several  leaves. 
The  fresh  material  is  to  be  placed  for  a  few  days  in  absolute 
alcohol,  and  the  .thin  sections  made  from  it  are  to  be  treated 
with  dilute  alcohol.  The  sections  are  then  to  be  placed  in 
concentrated  sulphuric  acid,  and  after  the  acid  has  removed  the 
cell-wall,  its  excess  is  to  be  withdrawn  by  means  of  a  pipette, 


1  Pringsheim's  Jahrbiicher,  1880,  p.  170. 

2  Philosophical  Transactions  Royal  Society,  1883,  clxxiv.  817. 
8  Botanisches  Centralblatt,  1883,  xiv.  89,  121. 


216  PROTOPLASM. 

and  the  preparation  very  carefully  washed.  The  application  of 
strong  glycerin  completes  the  treatment.  The  specimen  must 
not  be  removed  from  the  slide  during  the  whole  series  of  opera- 
tions. If  the  manipulation  has  been  careful  throughout,  the 
minute  threads  can  be  seen  passing  from  one  mass  of  protoplasm 
to  the  next. 

591.  The  directions  given  by  Strasburger  for  demonstrating 
the  continuit}T  of  protoplasm  are  as  follows  :  From  the  stem  of  a 
dicotyledonous  shrub  or  tree  (the  diameter  of  which  should  be 
at  least  a  centimeter)  Ihe  periderm  is  removed  by  a  knife,  and 
very  thin  tangential  longitudinal  sections  are  then  made  through 
the  soft  green  bark.  The  parenchyma  cells  which  are  inter- 
mingled with  the  liber  contain  more  or  less  chlorophyll,  and  may 
have  pits,  the  very  smallest  of  which  are  not  bordered  (see  268). 
If  the  first  sections  have  shown  in  any  case  that  these  cells  are 
furnished  with  pits,  others  are  then  prepared  and  placed  at  once 
in  a  drop  of  a  solution  of  iodine  (that  of  iodine  in  an  aqueous 
solution  of  potassic  iodide  is  best).  The  excess  of  the  solution 
is  at  once  removed  and  the  preparation  covered  with  a  glass 
cover.  At  the  edge  of  the  cover-glass  there  is  placed  a  drop 
of  concentrated  sulphuric  acid,  and  by  the  side  of  this  a  couple 
of  drops  of  dilute  sulphuric  acid ;  when  these  are  mingled  the 
mixture  is  allowed  to  flow  under  the  cover-glass,  while  a  bit  of 
filtering-paper  on  the  other  edge  of  the  glass  draws  it  through. 
The  specimen  becomes  dark  blue.  If  the  color  is  deep,  the  cover- 
glass  is  cautiously  lifted  and  the  preparation  is  then  thoroughly 
but  carefully  washed  in  water.  After  this  washing,  a  drop  of 
a  solution  of  anilin  blue  is  added,  whereby  the  object  becomes 
stained  ;  then,  after  washing  again,  a  little  glycerin 1  is  added, 
and  the  cover-glass  is  fastened  down  with  some  cement.  For 
the  examination  of  the  specimen  the  strongest  objectives  —  pref- 
erably the  so-called  "  homogeneous  immersion,"  employed  with 
cedar-oil  —  are  indispensable. 

Under  a  sufficiently  high  power  the  middle  lamella  of  the  wall 
is  seen  to  be  somewhat  swollen,  while  the  contents  of  the  cells 
are  contracted  and  colored.  The  periphery  of  the  individual 
protoplasmic  masses  in  the  cells  of  the  cortical  parenchyma  is 
smooth  on  that  face  which  was  in  contact  with  the  cell-wall  hav- 
ing very  small  pits ;  but  it  has  minute  protrusions  on  that  face 
which  was  next  the  bordered  pits.  Moreover,  the  protrusions 
in  contiguous  cells  are  exactly  opposite  each  other.  Between 

1  Strasburger  advises  the  addition  of  a  little  anilin  blue  to  the  glycerin. 


CONTINUITY   OP   PROTOPLASM   IN   CELLS.  217 

the  protrusions  at  the  bordered  pits  there  extend  extremely  deli- 
cate threads  of  protoplasm  which  have  a  granular  character. 
The  threads  are  somewhat  curved  (especially  the  outer  ones), 
and  are  slightly  swollen  in  the  middle.  In  peculiarly  good 
preparations  it  has  been  shown  that  there  is  an  apparent  inter- 
ruption at  the  middle  of  their  course,  but  that  at  this  break 
there  are  still  minute  filaments  which  serve  to  connect  them. 
From  these  and  kindred  observations  Strasburger  and  some 
others  have  adopted  the  view  that  there  is  such  a  degree  of 
continuity  between  the  protoplasmic  masses  in  the  cells  that 
they  form  throughout  the  plant  an  unbroken  whole.1 

592.  That  protoplasm  may  perhaps  occur  in  intercellular  spaces 
appears  from  the  observations  of  Russow 2  and  of  Berthold.8    To 
demonstrate  this,  one-year-old  twigs  of  Ligustrum  vulgare  are 
hardened  for  a  few  days  in  absolute  alcohol,  longitudinal  sections 
of  the  primary  cortex  placed  in  dilute  iodine  solution  (see  30), 
the  excess  of  iodine  removed,  and  dilute  sulphuric  acid  added. 
The  contents  of  the  cells  and  of  the  intercellular  spaces  will  then 
appear  as  }'ellowish-brown  masses. 

593.  That  protoplasm  can  in  some  cases  pass  through  an  im- 
perforate  cell- wall  appears  from  the  observation  of  Cornu,4  that 
in  the  formation  of  the  macroconidia  of  a  certain  Nectria  all  the 
protoplasm  of  the  five  or  six  cells  of  the  spore  emerges  to  form 
the  macroconidium,  which  arises  as  an  outgrowth  of  one  of  the 
cells  of  the  spore.    The  four  or  five  partition-walls  through  which 
the  protoplasm  must  pass  are,  however,  neither  dissolved  nor 
perforated. 

It  is  probable  that  a  striking  phenomenon  of  fertilization  in 
phaenogams,  namely,  the  complete  emptying  of  the  pollen-tube 
of  its  protoplasm^  see' "Fertilization")  without  apparent  break 
in  the  continuity  of  the  wall,  must  be  referred  to  the  same  pene- 
trative power  of  protoplasm. 

The  withdrawal  of  the  principal  part  of  the  protoplasmic 
matters  from  deciduous  leaves  before  the  fall  of  the  leaf  may  be 
perhaps  explained  in  the  same  way. 

Strasburger  cites  as  an  illustration  of  this  penetrative  power 
the  well-known  case  of  the  removal  of  protoplasmic  matters 

1  Das  botanische  Practicum,  1884,  p.  617.     Strasburger  :  Bau  und  Wachs- 
thum  der  Zellhaute,  1882,  p.  246.     Frommann  :  Beobaclitungen  iiber  Structur 
des  Protoplasma  der  Pflanzenzellen,  1880. 

2  Sitz.  der  Dorpater  Naturforscher-Gesellschaft,  1882,  p.  19. 
8  Berichte  der  deutschen  botanischen  Gesellschaft,  ii.  20. 

*  ^omptes  Rendus,  1877,  tome  Ixxxiv.  p.  133. 


218  PROTOPLASM. 

from  the  cells  around  the  buds  which  form  on  the  incised  leaves 
of  Begonia.1 

594.  The  relations  of  the  cell-wall  to  protoplasm  are  not  yet 
fullj*  understood ;  and  in  regard  to  some  of  them  there  exists 
among  botanists  considerable  diversity  of  opinion.      The  two 
principal  views  are  the  following:    1.  The  cell-wall  is  formed 
by  the  solidification  upon  the  exterior  of  a  protoplasmic  mass, 
of  matters  previously  dissolved  in  it.      The   pellicle  thus  pro- 
duced is  regarded  as  a  sort  of  excretion  (since  in  most  cases  it 
is  not  again  to  be  dissolved  and  emploj-ed  by  the  organism)  or 
as  a  secretion  (because  in  a  few  instances  it  can  be  dissolved 
and  utilized  a  second  time  b}-  the  plant).     The  substance  capa- 
ble of  thus  solidifying  upon  the  surface  of  protoplasm  consists  of 
cellulose  combined  with  water  and  a  small  amount  of  incombus- 
tible matters,  but  it  is  not  positively  known  in  what  condition 
these  were  previously  combined  in  the  protoplasm.      2.    The 
cell-wall  may  be  regarded  as  directty  produced  by  a  conversion 
of  the  outer  film  of  protoplasm  into  cellulose  with  which  some 
other  matters  are  intermingled.2 

595.  The  young  cell-wall 8  is  practically  a  homogeneous  film  of 
cellulose,  which  speedily  undergoes  changes  both  in  its  chemical 
and  physical  character.     In  many  of  the  lower  plants  the  wall 
differs  in  some  particulars  from  that  found  in  the  higher  plants 
(see  p.  29),  but  the  differences  need  not  enter  into  the  present 
description. 

596.  Two  views  are  held  respecting  the  mode  of  growth  of 
the  cell-wall.      The  first  may  be  regarded  as  based  upon  the 
hypothesis  of  Nageli  spoken  of  in  588.     From  some  of  the  mate- 
rials held  dissolved  in  the  adherent  film  of  water  around  each 
micella  new  micellae  of  cellulose  are  supposed  to  be  produced, 

1  "That  protoplasm  can  pass  through  closed  cell- walls  is  beyond  doubt " 
(Vines,  note  to  second  edition  of  Sachs's  Text-book,  p.  946). 

2  The  view  that  cellulose  is  a  kind  of  secretion  is  stated  at  great  length  in 
Hofmeister's  Pflanzenzelle,  and  in  several  communications  by  Sachs  in  Bola- 
nische  Zeitung.     The  second  view  is  given  by  Schmitz,  Sitz.  der  niederrhei- 
uischen  Gesellschaft  fur  Natur-  und  Heilkunde,  Bonn,  1880.     He  bases  his 
opinion  largely  upon  the  fact  that  in  some  cases  the  cells  gradually  become 
emptied  of  protoplasm  as  the  amount  of  cell-wall  increases,  and  upon  the  phe- 
nomena which  attend  the  increase  of  the  cell-wall  in  thickness. 

8  It  was  believed  by  some  of  the  earlier  phytotomists  that  the  cell-wall  was 
a  close,  firm  network  of  extremely  fine  fibres,  while  others  held  it  to  be  com- 
posed of  minute  granules.  In  these  explanations  of  structure  it  was  confessed 
that  the  ultimate  fibres,  or  ultimate  granules,  lie  quite  beyond  the  reach  of  the 
highest  powers  of  the  microscope. 


GROWTH   OP  THE   CELL-WALL.  219 

which  are  interpolated  between  the  old.  This  is  the  intussus- 
ception theory.  It  has  gradual^  displaced  an  older  theory, 
namely,  that  of  growth  by  apposition.  As  the  older  theoiy  was 
usually  held,  it  presented  two  modifications,1  —  one  that  the 
growth  of  a  cell- wall  in  thickness  takes  place  on  the  exterior  of 
the  wall,  so  that  in  a  stratified  wall  all  the  outermost  portions 
are  the  newer ;  the  other,  that  all  the  new  matter  is  laid  down 
upon  the  interior  of  the  old. 

The  apposition  theoiy  has  recentty  attracted  much  attention 
from  the  studies  of  Schmitz,  and  from  its  adoption  and  advocacy 
b}'  Strasburger.2  As  now  held  by  these  authors,  the  view  is  this  : 
stratified  and  other  cell-walls  grow  in  thickness  by  the  deposi- 
tion of  new  particles  upon  the  inner  face  of  the  cell,  much  as  a 
crystal  adds  new  particles  to  itself;  growth  in  surface  is  the  result 
of  a  simple  stretching  of  the  wall  by  the  pressure  of  the  con- 
tents upon  it. 

Any  solution  which  causes  a  shrinking  of  the  contents  of  the 
cell,  and  thus  diminishes  the  pressure  on  the  wall,  may  cause 
a  diminution  of  the  size  of  the  cell  itself.  The  bearing  of  this 
upon  the  turgescence  of  the  cell  will  be  again  adverted  to  under 
"  Properties  of  New  Cells  and  Tissues." 

To  the  physical  characters  of  cellulose  already  mentioned 
(see  129),  may  now  be  added  that  property  which  is  possessed 
also  by  many  other  organized  substances  ;  namely,  that  of  swell- 
ing greatly  when  placed  in  water.  The  wall  of  a  living  and  active 
cell  is  of  course  moist,  and  its  increase  in  size  on  the  addition  of 
more  water  is  seldom  marked ;  but  under  certain  circumstances 
the  amount  of  water  in  the  cell-wall  even  of  an  active  cell  may 
fall  below  its  usual  amount,  and  then  the  application  of  water 
will  cause  an  appreciable  change  of  bulk.  Such  change  in  the 
amount  of  water  may  take  place  with  great  rapidity  upon 
slight  external  disturbances,  such  as  shock :  in  these  cases,  the 
amount  of  water  in  the  protoplasm  in  contact  is  correspondingly 
modified. 

597.  Historical  note  regarding  protoplasm.  The  word  proto- 
plasm appears  first  in  a  memoir  by  Mohl,  in  1846,  "On  the 
Movement  of  Sap  in  the  Interior  of  Cells,"  which  deals,  however, 


1  For  an  account  of  the  two  modifications  of  the  apposition  theoiy,  the 
student  is  referred  to  Harting's  paper,  translated  in  Linnsea,  1846,  and  Mohl's, 
in  Botanische  Zeitung,  1846.     A  fair  statement  of  the  first  modification  is 
presented  in  Mulder's  Physiological  Chemistry. 

2  Strasburger  :  Ban  und  Wachsthum  der  Zellhaiite,  1882. 


220  PROTOPLASM. 

not  so  much  with  the  movement  of  what  would  to-day  be  called 
cell-sap,  as  with  the  general  behavior  of  all  the  motile  contents 
of  active  vegetable  cells.  After  showing  that  his  predecessors 
had  not  clearly  understood  the  important  part  played  in  the  life 
of  the  cell  by  the  viscous  matter  known  vaguely  up  to  that  time 
as  schleim,  or  mucus,  Mohl  points  out  the  essential  identity  of 
the  nucleus,  primordial  utricle,  and  the  basic  substance  filling  all 
but  the  sap-cavities  of  the  cell.  For  the  substance  which  is 
essential  to  the  formation  of  every  new  cell  and  to  the  develop- 
ment of  newly  formed  cells  he  proposed,  upon  physiological 
grounds,  the  significant  name  protoplasma. 

For  convenience  of  reference,  the  paragraph  in  which  the  word 
is  first  employed  is  here  given  :  — 

"  Da  wie  schon  bemerkt  diese  zahe  Flussigkeit  iiberall,  wo  Zellen 
entstehen  sollen,  den  ersten,  die  kiinftigen  Zellen  andeutenden  festen 
Bildungen  vorausgeht,  da  wir  ferner  annehraen  miissen,  dass  dieselbe 
das  Material  fur  die  Bildung  des  Nucleus  und  des  Primordialsclilauches 
liefert,  indem  diese  nicht  nur  in  der  niiclisteu  raumlichen  Verbiudung 
mit  derselben  stehen,  sondern  auch  auf  Jod  auf  analoge  Weise  reagiren, 
dass  also  ihre  Organisation  der  Process  ist,  welcher  die  Entstehung  der 
neuen  Zelle  einleitet,  so  mag  es  \vohl  gerechtfertigt  sein,  wenn  ich  zur 
Bezeiclmung  dieser  Substanz  eine  auf  diese  physiologische  Function 
sich  beziehende  Benenimng  in  dem  "\Vorte  Protoplasma  vorschlage."  1 

In  1835  Dujardin  described  a  contractile  substance  capable  of 
spontaneous  movement  in  certain  of  the  lower  animals,  to  which 
he  gave  the  name  Sarcode.  The  identity  of  Barcode  with  that 
substance  which  forms  the  essential  body  of  animal  cells  and 
with  the  protoplasm  of  vegetable  cells  was  suggested  by  several 
investigators  and  finally  demonstrated  by  Max  Schultze  in  1861.2 

Schwann,  even  as  early  as  1839,  pointed  out  various  analogies 
and  homologies  between  animal  and  vegetable  cells,  and  enun- 
ciated the  following  proposition :  animal  cells  are  completely- 
analogous  to  vegetable  cells,  and  are  quite  as  independent  in 
their  mode  of  growth.  The  bearing  of  Schultze's  demonstra- 
tion upon  the  foregoing  proposition  is  obvious.  Schwann 
instituted  also  certain  comparisons  between  the  mode  of  forma- 
tion of  cells  and  that  of  crystals  (tk  Microscopical  Researches 
into  the  Accordance  in  the  Structure  and  Growth  of  Animals 
and  Plants."  translated  by  Henry  Smith  for  the  Sydenham 
Society,  1847). 

1  Botanische  Zeitung,  184(3,  p.  75. 

2  Archiv  fur  Anatomie,  Physiologic,  und  wiss.  Medicin,  1861,  pp.  1-27,  and 
Das  Protoplasma  der  Khizopoden  und  der  Pflanzonzellen,  Leipzig,  18<>3. 


CHAPTER  VII. 

DIFFUSION,    OSMOSIS,    AND    ABSORPTION    OF    LIQUIDS. 
DIFFUSION  AND  OSMOSIS. 

598.  WHEN  two  liquids  which  are  not  miscible  —  for  instance, 
oil  and  water  —  are  shaken  together,  and  then  left  at  rest,  they 
will  separate  sooner  or  later,  according  to  their  specific  gravity. 
But  if  two  miscible  liquids  are  shaken  together,  they  remain  as  a 
homogeneous  mixture  no  matter  what  their  specific  gravity  may 
be.     Also  when  two  miscible  liquids  are  left  in  contact,  without 
any  agitation  they  become  thoroughly  commingled,  and  constitute 
a  uniform  mixture ;  this  uniform  commingling  of  two  or  more 
miscible  fluids  is  termed  diffusion.1 

599.  Furthermore,  if  two  miscible  liquids  are  separated  by 
a  membrane  which  can  be  moistened  by  them,  they  will  diffuse 
through  it  and  make  a  uniform  mixture.     This  latter  kind  of 
diffusion,  in  which  the  contact  between  the  two  liquids  is  not 
direct,  but  takes  place  through  a  septum  of  some  substance,  is 
known  as  osmosis.     In  the  plant  and  in  its  surroundings  the 
two  kinds  of  diffusion  play  such  an  important  part  that  they 
must  receive  special  attention. 

600.  Diffusion  of  liquids.      The  rate  of  diffusion  varies  with 
the  nature  of  the  liquids  and  the  temperature.    The  statements  in 
the  following  paragraphs  are  substantially  as  given  by  Graham.2 

1  Pfaundler  applies  this  term  to  the  commingling  whether  it  is  or  is  not 
brought  about  by  agitation  (Miiller's  Lehrbuch,  1877,  i.  162). 

2  They  are  based  upon  two  series  of  experiments  conducted  with  very  sim- 
ple apparatus.     In  the  first  series  a  small,  wide-mouthed  vial  containing  one 
liquid  was  placed  in  a  jar  holding  the  other  liquid,  allowed  to  stand  a  few 
days,  withdrawn,  and  the  amount  of  diffusion  noted.     In  the  second  series 
Graham  pursued  the  plan  of  placing  in  a  cylindrical  glass  jar,  152  mm.  high 
and  87  mm.  wide,  seven  tenths  of  a  liter  of  pure  water,  and  then  carefully  car- 
rying to  the  bottom  of  the  jar,  by  means  of  a  fine  pipette,  one  tenth  of  a  liter 
of  the  liquid  to  be  diffused.     The  jar  was  then  left  at  rest  in  an  apartment 
where  the  temperature  was  nearly  constant,  and  after  a  certain  time  its  contents 
were  drawn  off  carefully  in  portions  of  fifty  cubic  centimeters,  each  portion 
evaporated  separately,  and  the  residue  remaining  after  evaporation  weighed. 


222 


DIFFUSION  AND  OSMOSIS. 


601.  Different  salts  in  solutions  of  equal  strength  diffuse  in 
unequal  times.     Thus  potassic  hydrate  diffuses  with  double  the 
rate  of  potassic  sulphate,  and  the  latter  with  double  the  rate 
of  crystallized  sugar.     But  these  substances  have  a  compara- 
tively high   rate  of  diffusion.      A  solution  of  caramel  (sugar 
heated  till  it  becomes  brown)  diffuses  very  slowly  ;  the  sugar  in 
this  case  has  been  so  changed  in  its  character  that  its  rate  of 
diffusion  has  been  reduced  from  a  high  to  a  very  low  one.    Gela- 
tin may  be  taken  as  the  representative  of  the  almost  "  fixed  "  or 
slowly  diffusible  class  of  substances  ;  most  crystalline  substances, 
as  representatives  of  the  highly  diffusible  class.     The  former  are 
collectively  known  as  colloids  (K6XXa,  glue),  the  latter  as  crystal- 
loids.    It  must  be  noted  that  Graham's  use  of  this  word  "  crys- 
talloid" is  different  from  that  in  which  it  has  been  employed  in 
speaking  of  the  protein  bodies  (177). 

602.  With   each   salt  the   rate   of  diffusion   increases   at   a 
slightly  higher  rate  than  the  temperature  of  the  solution. 

603.  The  members  of  certain  chemical  groups  are  equally  dif- 
fusible.    Thus  hydrochloric,  hydrobromic,  and  hydriodic  acids ; 
the  chlorides,  bromides,  and  iodides  of  the  alkaline  metals,  etc., 
have  equal  rates  of  diffusion  into  pure  water. 

604.  The  diffusion  of  a  solution  of  a  salt  into  the  dilute  solution 
of  another  salt  takes  place  nearly  as  rapidl}'  as  into  pure  water ; 


The  difference  in  the  rates  of  diffusion  of  ten  per  cent  solutions  of  different 
substances  experimented  upon  in  the  manner  described  on  the  preceding  page 
is  clearly  shown  by  the  annexed  table. 


Number  of  stratum  from  above 
downwards. 

Sodic 
Chloride. 

Sugar. 

Gum. 

Tannin. 

1    
2 

.104 
129 

.005 
008 

.003 
003 

.003 
003 

3             .         . 

162 

012 

003 

004 

4 

198 

016 

004 

003 

5 

267 

030 

003 

005 

g 

340 

059 

004 

007 

7    

.429 

.102 

.006 

.017 

8    
9    
10    
11    
12    
13    

.635 
.654 
.766 
.881 
.991 
1  090 

.180 
.305 
.495 
.740 
1.075 
1  435 

.031 
.097 
.215 
407 
.734 
1  157 

.031 
.069 
.145 
.288 
.656 
1  050 

14    
15,  16  

1.187 
2.266 

1.758 
3.783 

1.731 
6.601 

1.719 
6.097 

9.999 

10.003 

9.999 

9.997 

The  first  series  of  experiments  are  described  in  Philosophical  Transactions, 
1850;  the  second,  in  1861. 


BATES   OF  DIFFUSION.  223 

but  if  the  second  solution  contains  some  of  the  salt,  like  that  in 
the  first  solution,  the  rate  of  diffusion  is  retarded. 

605.  The  rate  with  which  a  salt  passes  from  a  stronger  into 
a  more  dilute  solution  is  nearly  proportional  to  the  degree  of 
concentration.     The  approximate  times  required  for  the  diffu- 
sion of  equal  weights  of  various  substances  into  water  are  given 
in  the  following  table :  — 

Hydrochloric  acid 1. 

Sodic  chloride 2.33 

Magnesic  sulphate 7. 

Cane-sugar 7. 

Albumin 49. 

Caramel 98. 

606.  Of  the  colloids,  Graham  says:1  "Low  diffusibility  is 
not  the  only  property  which  the  bodies  last  enumerated  possess 
in  common.   .  .   .  Although  often  largely  soluble  in  water,  they 

1  Philosophical  Transactions,  1861. 

Graham  says  further  :  "Although  chemically  inert  in  the  ordinaiy  sense, 
colloids  possess  a  compensating  activity  of  their  own  arising  out  of  their 
physical  properties.  While  the  rigidity  of  the  crystalline  structure  shuts  out 
external  impressions,  the  softness  of  the  gelatinous  colloid  partakes  of  fluidity, 
and  enables  the  colloid  to  become  a  medium  for  liquid  diffusion,  like  water 
itself.  The  same  penetrability  appears  to  take  the  form  of  cementation  in  such 
colloids  as  can  exist  at  a  high  temperature.  Hence  a  wide  sensibility  on  the 
part  of  colloids  to  external  agents.  Another  and  eminently  characteristic  qual- 
ity of  colloids  is  their  mutability.  Their  existence  is  a  continued  metastasis. 
A  colloid  may  be  compared  in  this  respect  to  water  while  existing  liquid  at  a 
temperature  under  its  usual  freezing  point,  or  to  a  supersaturated  saline  solu- 
tion. Fluid  colloids  appear  to  have  always  a  pectous  modification  (irt)KTfa, 
curdled),  as  fibrin,  casein,  albumin.  But  certain  liquid  colloid  substances  are 
capable  of  forming  a  jelly,  and  yet  still  remain  liquefiable  by  heat  and  soluble 
in  water.  Such  is  gelatin  itself,  which  is  not  pectous  in  the  condition  of  ani- 
mal jelly,  but  may  be  so  as  it  exists  in  the  gelatiferous  tissues.  Colloids 
often  pass  under  the  slightest  influences  from  the  first  into  the  second  condi- 
tion. The  solution  of  hydrated  silicic  acid,  for  instance,  is  easily  obtained  in 
a  state  of  purity,  but  it  cannot  be  preserved.  It  may  remain  fluid  for  days  or 
weeks  in  a  sealed  tube,  but  is  sure  to  gelatinize  and  become  insoluble  at  last. 
Nor  does  the  change  of  this  colloid  appear  to  stop  at  that  point.  For  the 
mineral  forms  of  silicic  acid,  deposited  from  water,  such  as  flint,  are  often 
found  to  have  passed  during  the  geological  ages  of  their  existence,  from  the 
vitreous  or  colloidal  into  the  crystalline  condition  (H.  Rose).  The  colloidal 
is,  in  fact,  a  dynamical  state  of  matter  ;  the  crystalloidal  being  the  statical 
condition.  The  colloid  possesses  energia.  It  may  be  looked  upon  as  the 
probable  primary  source  of  the  force  appearing  in  the  phenomena  of  vitality. 
To  the  gradual  manner  in  which  colloidal  changes  take  place  (for  they  always 
demand  time  as  an  element),  may  the  characteristic  protraction  of  chemico- 
organic  changes  also  be  referred." 


224  DIFFUSION   AND   OSMOSIS. 

are  held  in  solution  by  a  most  feeble  force.  The}'  appear  singu- 
larly inert  in  the  capacity  of  acids  and  bases,  and  in  all  the  ordi- 
nary chemical  relations.  But,  on  the  other  hand,  their  peculiar 
physical  aggregation  with  the  chemical  indifference  referred  to, 
appears  to  be  required  in  substances  that  can  intervene  in  the 
organic  processes  of  life.  The  plastic  elements  of  the  animal 
body  are  found  in  this  class." 

607.  Osmose,  or  Osmosis.     Diffusion  of  liquids  through  mem- 
branes.    The  interposition  of  a  permeable  septum  between  mis- 
cible  liquids  does  not  prevent  diffusion.     Thus  if  a  solution  of 
sodic  chloride  is  separated  from  pure  water  by  an  intervening 
membrane,  as  one  of  bladder  or  of  vegetable  parchment  (see 
page  32),  diffusion  takes  place  in  about  the  same  time  as  if  no 
membrane  were  present. 

608.  For  most  experiments  in  osmosis  the  simple  apparatus 
known  as  an  osmometer  answers  very  well.     It  consists  of  a 
small  reservoir  furnished  with  a  membrane  bottom,  and  a  gradu- 
ated tube  at  its  upper  part.     A  very  good  osmometer  can  be 
prepared  from  a  short-necked  bottle  from  which  the  bottom  has 
been  carefully  removed.      After  the  edges  at  the  bottom  have 
been  made  smooth,  a  piece  of  wet  parchment  paper  is  tightly 
fastened  on  by  waxed  thread.     Great  care  must  be  taken  to 
select  parchment  or  parchment  paper  which  is  free  from  perfora- 
tions,1 and  the  tube  at  the  neck  must  be  well  fitted  to  a  velvet 
cork,  so  that  no  escape  of  liquid  can  take  place  in  any  way.     A 
film  of  ordinary  unsized  paper  evenly  covered  with  a  solution  of 
warm  gelatin,  which  cools  to  form  a  firm  mass  upon  its  surface, 
makes  a  good  substitute  for  parchment  in  this  apparatus.     A 
thin  film  of  white  of  egg  coagulated  by  heat  will  also  serve  well 
for  a  covering. 

609.  The  osmometer,  filled  to  a  certain  point  on  the  tube  with 
the  liquid  to  be  experimented  upon,  is  suspended  in  pure  water  so 
that  the  liquid  in  the  apparatus  is  on  exactly  the  same  level  as 
the  water.     It  will  be  seen  b}-  the  experiment  that  not  only  does 
diffusion  take  place,  but  that  there  is  a  change  in  the  level  of 
the  liquid  in  the  tube. 

610.  When  an}'  of  the  more  diffusible  substances  are  placed 
in  a  state  of  solution  in  the  reservoir,  a  small  amount  of  the 
crystalloid   passes  outwards,   while  a  much   larger   amount  of 

1  The  existence  of  actual  perforations  in  good  parchment  can  be  demon- 
strated by  subjecting  the  apparatus  to  pressure,  or  even  by  repeatedly  wiping 
the  exposed  surface  of  the  parchment  with  filtering-paper. 


PRECIPITATION-MEMBRANES.  225 

water  passes  inwards.  The  change  of  level  caused  is  of  course 
accompanied  by  an  immediate  change  in  the  hydrostatic  pres- 
sure, and  hence  water  should  be  added  to  or  removed  from  the 
outer  vessel,  to  balance  inequalities  of  height  as  fast  as  thev 
occur. 

611.  The  proportional  amounts  of    the    substances    inter- 
changed have  been  determined  by  various  observers.      Jolly,1 
by  an  ingenious  modification  of  the  osmometer,  obtained  the 
following  results ;  the  figures  representing  the  weight  of  water 
which  replaced  in  osmosis  one  part  by  weight  of  the  substance : 

Sodic  chloride 4.3 

Sugar 7.1 

Sodic  sulphate 11.6 

Magnesic  sulphate 11.6 

Potassic  sulphate 12. 

Potassic  hydrate 215.7 

612.  These  figures  are  known  as  the  osmotic  equivalents  of 
the  respective  substances,  but  they  are  by  no  means  constant ; 
since,  as  Ludwig2  has  shown,  they  depend  partly  on  the  de- 
gree of  concentration  of  the  solution  used,  the  duration  of  the 
experiment,  and  the  character  of  the  membrane. 

613.  If,  however,  a  colloidal  body  is  placed  in  the  reservoir, 
very  little  comparatively  passes  outwards,  and  in  the  case  of 
some  colloids  nothing.     "  Indeed,  an  insoluble  colloid,  such  as 
gum-tragacanth,  placed  in  powder  within  the  osmometer,  was 
found  to  indicate  the  rapid  entrance  of  water,  to  convert  the 
gum  into  a  bulky  gelatinous  hydrate.     Here,   no  outward  or 
double  movement  is  possible."3     This  very  important  fact  must 
be  borne  in  mind  in  the  application  of  the  phenomena  of  os- 
mose to  those  of  absorption  of  liquids  by  the  colloids  in  active 
vegetable  cells. 

614.  Precipitation-membranes.     Traube4  (in  1867)  discovered 
that  when  a  drop  of  a  solution  of  copper-sulphate  is  placed  in 
a  solution  of  potassic  ferroc3-anide,  there  is  produced  over  its 
whole  surface  a  coherent  membrane  (of  precipitated  cupric  ferro- 
cyanide),  known  as  a  "  precipitation-membrane."     This  at  once 
begins  to  increase  in  size,  but  somewhat  irregularly,  as  if  breaks 
occurred  at  the  upper  part  through  which  a  portion  of  the  liquid 

1  Zeitschrift  fur  rationelle  Medicin,  1849,  vii.  p.  83. 

2  Poggendorff  :  Annalen  der  Physik  und  Chemie,  Ixxviii.  p.  307. 

3  Graham  :  Journ.  Chem.  Soc.,  1862,  p.  269. 

4  Archiv  fur  Anat.  u.  Physiol.  du  Bois-Reyuiond  u.  Reichert,  1867,  p.  87. 

15 


226  DIFFUSION    AND   OSMOSIS. 

within  flowed  out  only  to  meet  the  exterior  liquid,  and  there 
formed  instantly  a  precipitate  cohering  with  the  edges  of  the 
rupture.  If  a  fragment  of  chloride  of  copper  is  placed  in  a  test- 
tube  containing  a  strong  solution  of  potassic  ferrocyanide,  the 
action  is  more  rapid  than  with  copper- sulphate.  The  fragment 
dissolves  at  once,  and  forms  a  green  globule  at  the  bottom  of 
the  tube.  If  it  now  be  carefully  watched,  it  will  be  seen  that  a 
delicate  transparent  film  (the  precipitate  of  cupric  ferrocyauide, 
which  in  a  flocculeut  state  is  brown)  is  produced  over  the  glob- 
ule, and  the  sphere  begins  at  once  to  grow  into  a  cylindrical 
bod}7.  The  liquid  in  the  upper  part  of  the  closed  cylinder  is 
almost  colorless ;  that  at  the  bottom  is  deep  green.  The  inter- 
mittent growth  in  height  appears  to  admit  of  only  one  explana- 
tion ;  namely,  that  the  membrane  is  torn  by  the  great  pressure 
within,  and  the  solution  of  copper  chloride  which  flows  through 
is  immediately  covered  by  a  newly  formed  film.  Bj-  careful 
management,  such  growths  of  cylindrical  form  can  be  produced 
several  inches  long. 

Traube  also  discovered  that  when  a  drop  of  /?  gelatin  (gelatin 
which  has  been  boiled  continuously  for  about  three  days,  there- 
by losing  its  power  of  coagulation)  is  placed  in  a  solution  of 
tannin,  a  film  forms  at  once,  which  begins  to  grow  into  a  spheri- 
cal cell,  but  without  the  appearance  of  irregular  and  intermit- 
tent rupture.  Such  an  artificial  cell  is  best  prepared  by  placing 
a  glass  tube  having  a  drop  of  ft  gelatin  on  the  tip  into  a  solution 
of  tannin.  Its  growth  is  even  and  uninterrupted,  and  unless 
the  apparatus  is  disturbed,  no  appearance  of  rupture  is  observed. 
A  further  discovery  was  made  by  Traube ;  namely,  that  a  co- 
herent film  may  be  formed  even  by  the  contact  of  pure  water. 
The  coagulum  produced  when  gelatin  is  acted  on  by  tannin  (the 
so-called  tannate  of  gelatin)  is  soluble  in  a  concentrated  solution 
of  tannin,  but  is  insoluble  in  a  dilute  solution.  If  a  drop  of  a 
solution  of  tannate  of  gelatin  thus  prepared  is  placed  in  pure 
water,  a  coherent  film  forms  at  the  surface  which  can  increase 
up  to  a  certain  size.1 

615.  Pfefler  has  employed  the  precipitation-membranes  dis- 
covered by  Traube,  in  an  ingenious  apparatus  b}-  which. the 
pressure  developed  in  the  so-called  artificial  cell  can  be  accu- 
rately measured.  The  apparatus  consists  of  a  porous  porcelain 


1  At  this  point  should  be  mentioned  the  observation  of  Nageli,  that  when- 
ever cell-contents  rich  in  protein  matters  come  in  contact  with  watery  media,  a 
membranous  film  is  formed  over  the  surface  (1'flanzenphysiologische  Unter- 
guchungen,  1355,  pp.  9,  10). 


EXPERIMENTS   OF   PFEFFER. 


227 


or  clay  cell,  like  those  which  are  used  in  the  Bunsen  battery, 
connected  by  means  of  a  glass  collar  with  a  suitable  manometer. 
Within  the  clay  cell  a  precipitation  film  is  formed  ; 1  the  cell  is 

1  The  following  account  of  details  essential  to  success  in  these  experiments 
of  Prof.  Pfeffer  has  been  prepared  by  one  of  his  students,  Dr.  W.  P.  Wilson. 

The  principal  portion  of  the  apparatus  is  a  porous  porcelain  cell,  z,  46  mm. 
high  and  16  mm.  in  diameter,  with  walls  l£  mm.  in  thickness.  This  cell  is 
cemented  on  to  a  piece  of  glass  tubing,  v.  A  second  piece  of  tubing,  t,  with 
lateral  tube,  is  cemented  into  the  first  piece.  The  lateral  opening  is  for  the 
manometer  m,  the  one  at  g  is  for  the  convenience  of  filling  and  sealing  th« 
cell. 

One  of  the  two  fluids  used  in  forming  the 
membrane  for  experimentation  is  allowed 
to  penetrate  the  porous  cell  from  without. 
When  this  has  thoroughly  taken  place,  the 
second  fluid  is  poured  into  the  interior.  The 
contact  of  the  two  fluids  takes  place,  there- 
fore, on  the  inner  surface  of  the  porous  cell, 
and  here  the  precipitate  is  formed  which  is 
termed  the  pellicle-membrane  or  precipita- 
tion-membrane. Substances  which  by  their 
mutual  contact  give  rise  to  such  precipitation- 
membranes  are  termed  membranogenic.  It 
will  readily  be  seen  that  during  any  internal 
pressure  the  porous  porcelain  cell  acts  as  a 
support  for  the  membrane.  If  the  exterior 
solution  is  copper-sulphate,  the  interior  solu- 
tion potassic  ferrocyanide,  then  the  precipi- 
tated membrane  will  be  cupric  ferrocyanide. 
After  the  membrane  has  been  formed,  then 
any  solution  not  chemically  incompatible 
with  it  may  be  employed  in  the  cell ;  namely, 
syrup  from  cane-sugar,  a  solution  of  saltpetre, 
or  a  still  stronger  solution  of  potassic  ferro- 
cyanide than  was  used  in  the  preparation  of 
the  cell. 

As  the  successful  working  of  the  apparatus 

depends  upon  the  exact  carrying  out  of  quite  a  number  of  minor  details,  the 
following  description  of  the  methods  of  putting  the  parts  together  may  be 
found  useful :  — 

In  order  to  insure  absolute  freedom  from  any  foreign  substance,  the  porcelain 
cell  must  be  successively  washed  in  dilute  solutions  of  potassic  hydrate  and 
hydrochloric  acid,  and  then  thoroughly  dried.  Warm  a  piece  of  sealing-wax 
in  the  spirit-lamp  and  draw  it  to  a  point.  Slowly  heat  the  open  end  of  the 
cell  in  the  alcoholic  flame.  When  hot  enough  to  very  readily  melt  the  wax, 
apply  the  point;  and  while  the  cell  is  continually  rotating,  cover  evenly  a  space 
to  the  depth  of  15  mm.  with  wax  in  the  interior.  It  should  be  about  2  mm. 
in  thickness.  Pick  up  the  short  piece  of  tubing,  v,  which  has  been  previously 
waxed  on  one  end,  and  rotate  it  over  the  flame.  When  both  porcelain  cell  and 
glass  tube  are  as  warm  as  they  can  be  made  and  yet  the  wax  kept  smooth 


228  DIFFUSION   AND   OSMOSIS. 

then  filled  with  any  diffusible  liquid,  —  for  instance,  a  dilute  solu- 
tion of  sugar,  —  the  manometer  is  attached,  and  the  whole  appa- 
ratus is  placed  in  pure  water  or  an}'  aqueous  solution. 


and  even  on  all  sides,  place  them  quickly  together,  lapping  about  15  mm., 
and  continue  the  rotary  motion  until  cool.  Take  a  scalpel  with  a  point  bent 
at  right  angles  to  the  blade,  heat  it,  and,  inserting  it  in  the  glass  tube, 
cut  away  the  wax  at  its  inner  end,  thus  exposing  a  shoulder  of  the  thickness 
of  the  glass.  Roll  out  in  the  form  of  a  pencil  about  2  mm.  in  diameter  a  piece 
of  sealing-wax  which  has  been  made  a  little  soft  by  the  addition  of  a  drop  or 
two  of  turpentine.  A  piece  of  this,  equal  in  length  to  the  inner  circumference 
of  the  glass  tube,  in  a  long  coil,  should  be  placed  on  the  point  of  the  scalpel, 
carried  in  to  the  shoulder  and  pressed  into  it.  A  little  heat  very  cautiously 
applied  from  without,  with  proper  turning  of  the  cell,  will  easily  cause  this 
softer  wax  to  flow  and  fill  the  shoulder  with  perfect  smoothness.  The  use  of 
the  softer  sealing-wax  makes  a  joint  which  will  not  crack  under  strong  pres- 
sure. Now  cement  the  tube  t  very  firmly  into  v,  with  the  same  precautions 
as  above.  Unless  a  pressure  of  more  than  three  atmospheres  is  desired,  the 
soft  wax  need  not  here  be  used. 

The  cell  is  now  ready  to  be  prepared  for  filling.  In  order  to  saturate  the 
porous  porcelain  with  any  given  solution,  the  air  must  first  be  wholly  removed. 
Place  the  apparatus  in  a  beaker  of  water  which  has  been  freed  from  air  by  boil- 
ing, and  set  the  whole  under  the  bell-jar  of  an  air-pump.  Exhaust  and  admit 
the  air  into  the  bell-jar  repeatedly  until  bubbles  can  no  longer  be  seen  to  rise 
from  the  porcelain.  Transfer  the  cell  to  a  three  per  cent  solution  of  copper- 
sulphate,  and  exhaust  the  air  again.  Four  or  five  hours  will  be  required  for 
this  solution  to  thoroughly  penetrate  the  porous  cell.  At  the  end  of  this  time 
remove  it  from  the  copper-sulphate,  empty  it,  and  with  some  long  twisted 
strips  of  bibulous  paper  quickly  dry  up  all  moisture  from  its  inner  surface.  If 
at  any  time  the  exterior  surface  of  the  cell  begins  to  appear  dry  before  the 
moisture  from  within  has  been  wholly  removed,  dip  it  at  once  in  the  solution 
from  whence  it  came.  At  the  moment  when  the  moisture  is  properly  removed, 
fill  the  cell  to  the  second  joint  with  a  three  per  cent  solution  of  potassic  ferro- 
cyauide  and  replace  it  in  the  copper-sulphate,  taking  care  that  the  surfaces  of 
the  two  fluids  are  in  the  same  plane.  An  interim  of  at  least  twelve  hours  must 
now  elapse  in  order  that  the  membrane  may  be  properly  formed.  At  the  end  of 
this  time  the  cell  is  ready  to  be  used,  either  with  the  solution  which  it  already 
contains  or  with  some  other.  If  some  other  solution  is  to  be  employed,  then 
carefully  empty  out  the  potassic  ferrocyanide,  and  after  washing  the  cell  with 
a  little  distilled  water,  fill  it  with  the  fluid  to  be  used. 

The  cell  must  be  so  filled  and  sealed  as  to  leave  absolutely  no  air  within, 
otherwise  the  pressure  cannot  be  accurately  measured.  Insert  a  perforated 
rubber  cork  at  g.  Fill  the  manometer  from  the  quicksilver  to  the  extremity 
of  the  tube  with  potassic  ferrocyanide,  or  whatever  other  solution  is  to  be 
used  in  its  place,  and  push  it  into  position  in  the  cork.  Fill  the  cell  com- 
pletely full,  and  press  firmly  into  place  the  second  perforated  cork,  taking 
great  care,  first,  that  no  bubble  of  air  remains  at  its  base  ;  and  second,  that 
not  a  particle  of  potassic  ferrocyanide  comes  in  contact  with  the  outside  of 
the  cell. 

A  bent  glass  tube,  drawn  to  a  capillary  point  at  one  end,  should  now  be 
filled  with  potassic  ferrocyanide  and  slowly  pushed  into  the  cork.  If  this  is 


TiiE   CELL   AN    OSMOTIC   APPARATUS. 


21:0 


In  certain  experiments  by  Pfeffer,  made  with  a  single  cell,  in 
which  was  a  solution  of  cane-sugar  containing  a  trace  of  one  of 
the  membranogenic  substances,  while  the  water  outside  contained 
a  trace  of  the  other,  the  following  pressures  were  indicated  :  — 


Percentage  of  sugar  in  the 
solution,  by  weight. 

Temperature. 

Mercurial  pressure. 

1 

13°.7  C. 

53.8  cm. 

1 

13.6 

53.2   ' 

2 

14. 

101.6   ' 

4 

13.8 

208.2   • 

6 

14.7 

307.5   ' 

1 

14.6 

53.5   ' 

With  a  3.3  per  cent  solution'  of  potassic  nitrate  in  the  ceil, 
Pfeffer  obtained  a  mercurial  pressure  of  436.8  cm. 

616.  An  active  vegetable  cell  is  an  osmotic  apparatus.  The 
chief  agent  in  its  work  of  absorption  is  the  peripheral  film  of 
the  colloidal  protoplasmic  mass,  and  this  receives  mechanical 
support  from  the  wall  of  cellulose  in  which  it  is  held.  It  was 
formerly  believed  that  in  osmosis  there  is  always  an  exchange 
of  materials,  one  current  passing  inwards  (cndosmose),  the 
other  outwards  (exosmose)  ;  and  there  are  numerous  cases  in 
which  this  is  true,  and  in  which  the  osmotic  equivalent  can  be 
calculated  (see  612).  But  Pfeffer's  experiments  show  how  great 
a  force  may  be  exerted  by  osmosis  in  cases  in  which  there  is 
little  or  no  substance  passing  out  to  replace  the  liquid  ab- 
sorbed. In  the  series  of  experiments  in  which  a  solution  of 
sugar  was  employed  in  his  osmotic  apparatus,  no  trace  of  this 


properly  done,  any  small  quantity  of  air  which  may  be  in  the  upper  part  of  the 
cork  will  rise  during  insertion  to  the  capillary  point.  Gradually  and  cautiously 
warm  the  tube,  beginning  close  to  the  cork.  This  will  expand  the  fluid  and 
drive  the  air  wholly  out.  At  the  moment  when  the.  solution  completely  fills 
the  tube,  fuse  the  capillary  point  in  the  spirit-lamp.  The  cell  is  now  entirely 
free  from  air  and  hermetically  scaled.  During  the  time  of  inserting  the  ma- 
nometer, corking,  and  sealing,  the  porcelain  part  of  the  cell  must  not  be  allowed 
to  become  dry.  but  must  be  frequently  dipped  into  the  solution  from  which  it 
was  taken.  With  unannealed  brass  wire  secure  both  corks  after  the  fashion 
of  champagne-bottles. 

Now  suspend  the  cell  in  the  solution  of  copper  sulphate  so  that  the  porce- 
lain shall  be  wholly  submerged  but  shall  not  touch  the  sides  of  the  vessel 
containing  the  solution.  Note  the  position  of  the  mercury  in  the  manometer, 
and  see  that  the  temperature  remains  constant  in  the  room.  If  the  cell  is 
perfect,  a  certain  degree  of  pressure  will  be  indicated  in  less  than  an  hour. 


230          ABSORPTION   OF   LIQUIDS    THROUGH   ROOTS. 

substance  could  afterwards  be  discovered  in  the  water  on  the 
outside.  The  apparatus  lined  with  its  colloidal  film,  containing 
a  small  amount  of  saccharine  solution,  and  surrounded  by  a  very 
dilute  aqueous  solution  of  mineral  matters,  is  an  instructive 
imitation  of  a  vegetable  cell. 

ABSORPTION  OF   LIQUIDS  THROUGH   ROOTS. 

617.  Submerged  aquatics  may  absorb  with  their  whole  surface. 
They  are  bathed  in  dilute  saline  solutions  containing  the  gases 
essential  to  vegetative  activity,  and  the  materials  for  their  food 
can  be  taken  from  the  medium  surrounding  them,  perhaps  quite 
as  well  b}'  one  of  their  parts  as  by  another.   This  fact  is  well  illus- 
trated by  the  larger  algie,  in  which  the  organs  popularly  called 
roots  are  merely  mechanical  hold-fasts,  and  the  work  of  absorp- 
tion can  proceed  at  any  part  of  the  frond.     The  simplest  differ- 
entiation of  organs  for  absorption  is  met  with  in  the  rhizoids  or 
complex  root-hairs  of  mosses,  and  in  the  filaments  of  fungi  which 
bury  themselves  in  a  nutrient  substratum.     Above  the  mosses 
the  differentiation  of  organs  into  roots  for  absorption,  and  stems 
for  the  support  of  the  assimilative  tissue,  is  very  plain.     For  our 
present  purpose  it  is  best  to  begin  an  examination  of  the  absorp- 
tion of  liquids  by  plants  with  a  study  of  the  structure  and  the 
office  of  the  root. 

618.  It  has  been  shown  in  Part  I.  that  the  younger  parts  of 
the  root  are    clothed  with    extremely  delicate  epidermal  cells, 
which,  with  the  slender  trichomes  associated  with  them,  con- 
stitute the  absorbing  apparatus  of  the  plant.     (These  epider- 
mal cells  of  the  root,  taken  collectively,  have  been  called  the 
Epiblema.1) 

619.  The  root- tip  with  its  protective  cap  does  not  share  to 
any  great  extent,  if  indeed  at  all,  in  the  work  of  absorption  ; 
and  yet  to  the  soft,  spongy,  rounded  mass  of  tissue  forming  the 
root-tip  was  formerly  given  the  name  of  spongiole,  on  account 
of  its  spongy  nature,  and  its  supposed  office  of  sucking  up  nu- 
trient matters  from  the  soil.2 

1  This  term,  early  introduced,  was  retained  by  Schleiden  :   Principles  of 
Scientific  Botany,  1849,  pp.  68,  218. 

2  Thus  De  Camlolle,  in  his  Physiologic  Vegetale,  1832,  p.  41,  says:  "La 
succion  des  racines  s'execute  par  des  points  speoiaux  qu'on  nomme  spongioles, 
qui  sont  corn  poses  d'un  tissu  cellulaire  tres-fiu  et  toujours  nouveau,  puisque  les 
racines  s'alongent  sans  cesse  par  leur  extremite.     L«  liquide  de  la  terre  tend 
a  entrer  dans  les  meats  de  ce  tissu  :    I.  par  la  force  de  capillarite  ;   II.  par 


ROOT-HAIRS.  231 

620.  Root-hairs.     It  was  shown  experimentally  by  Ohlert1  in 
1837,  that  the  tip  of  the  root  is  not  the  absorbing  part.     By 
careful  excision  of  the  tip,  and  the  use  of  a  harmless  water- 
proof varnish  to  cover  the  wound  caused,  he  obtained  full  absorp- 
tion of  liquids  through  the  sides,  and  not  the  end  of  a  young 
root.     He  further  demonstrated  the  very  general  occurrence  of 
delicate  hairs  upon  the  sides  of  young  roots,  and  expressed  the 
opinion  that  these  were  the  efficient  agents  in  root  absorption. 

621.  That  the  abundance  of  the  hairs  on  new  roots  is  depend- 
ent largely  on  the  amount  of  moisture  to  which  they  are  ex- 
posed, appears  from  experiments  on  the  roots  of  some  of  the 
more  common  cultivated  plants,  —  Allium  Cepa,  Cucurbita  Pepo, 
Zea  Mais,  etc.     In  all  these  cases  the  plant  can  almost  be  said 
to  regulate  the  amount  of  its  absorbing  surface  by  the  amount 
of  moisture  within  its  reach,  and  it  is  thought  by  some  that  all 
the  epidermal  cells  of  a  young  and  developing  root  have  the 
power  of  extending  into  hairs.      The  number  of  hairs  to  the 
square  millimeter  on  a  root  of  Zea  Mais  grown  in  a  moist  place 
was  found   by  Schwarz  to  be  425  ;    and  on  a  root  of  Pisum 
sativum,  232*. 

622.  Root-hairs  are,  as  has  been  shown  in  Part  I.,  cylindrical 
protuberances  from  the  external  wall  of  the  epidermal  cells. 
They  vary  in  length  from  .1  mm.  to  8  mm.     The  former  length 
occurs  in  a  few  grasses,  the  latter  in  some  water  plants.    Schwarz 
gives  the  following  measurements  of  length  :  root-hairs  of  Pota- 
mogeton,  5  mm. ;  of  Anacharis,  4  mm. ;  of  Brassica  Napus  in 
moist  air,  3  mm.  ;  of  Pisum  sativum  and  Avena  sativa,  2.5  mm. ; 
of  Vicia  Faba,  8  mm. 

623.  When  root-hairs  are  developed  in  contact  with  soil,  they 
become  much  distorted  (see  Fig.  89),  and  generally  dwarfed; 
they  curve  more  or  less  irregularly  around  the  particles  of  soil, 
and  frequently  are  enlarged  at  the  immediate  place  of  contact. 
Moreover,  the  character  of  the  cell-wall  is  somewhat  changed  at 
the  place  of  contact  with  the  particles ;  in  many  instances  the 
wall  undergoes  a  sort  of  mucilaginous  modification,  and  becomes 
so  firmly  united  to  the  particles  that  these  cannot  be  removed 

1'hygroscopicite.  Ces  deux  proprietes  de  tissu  peuvent  bien  expliquer  I'enorme 
quantite  d'eau  qni  penetre  dans  la  plante  vivante,  les  variations  de  cette  quan- 
tite selou  les  especes,  les  saisons,  etc.  II  so'uffit  d'admettre  que  les  cellules  des 
spongioles  donees  de  contractions  alternatives,  augmentent  et  diminuent  alter- 
nativement  les  meats  intercellulaires,  et  tendent  ainsi  a  absorber  de  1'eau  en 
quantite  proportionnee  a  la  force  et  a  la  rapidite  de  leurs  contractions  vitales. " 
1  Linnaea,  1837. 


282         ABSORPTION   OF  LIQUIDS   THROUGH   ROOTS. 

without  laceration  of  the  delicate  cells.  Notwithstanding  the 
extreme  tenuity  of  the  cell-wall,  it  is  thought  by  some  to  play  an 
important  mechanical  part  in  fastening  the  roots  in  the  soil.1 

624.  That  the  hairs  upon  the  root  vastly  increase  its  absorb- 
ing surface  is  self-evident.     Schwar/  has  shown  that  in  Indian 
corn  grown  in  moist  air  the  surface  presented  by  the  velvety 
hairs  which  cover  the  young  roots  is  5.5  times  greater  than  that 
of  the  part  of  the  root  on  which  the  hairs  occur ;  while  the  ratio 
of  these  surfaces  in  the  roots  of  peas  is  as  12.4  to  1 ;  and  in  the 
aerial  roots  of  Scindapsus  pinnatus,  as  18.7  to  1.     But  all  these 
figures,  which  are  at  best  only  approximate,  appear  to  be  very  low. 

625.  Extent  of  Root-systems.      In   extending,    the   root,   by 
growth  at  its  protected  extremity,  can  insinuate  itself  between 
particles  of  soil  which  could  not  be  easily  displaced  by  simple 
thrust.    The  branches  from  the  main  root  extend  exactly  as  does 
the  main  root  itself,  —  by  continual  additions  just  behind  the 
tip,  —  and  the  area  covered  by  a  root-system  finally  becomes 
very  large.    One  of  the  earliest  recorded  measurements  is  that  by 
Hales,2  who  estimated  that  the  roots  of  a  sunflower  (3£  ft.  high), 
taken  together,  were  no  less  than  1,448  feet  in  length.    The  plant 
had  ''eight  main  roots  reaching  fifteen  inches  deep,  and  side- 
ways from  the  stem  ;  it  had,  besides,  a  very  thick  bush  of  lateral 
roots,  which  extended  every  way  in  a  hemisphere  about  nine 
inches  from  the  stem  and  main  roots." 

626.  Nobbe  has  shown  that  in  year-old  plants   of  certain 
closely  allied  gymnosperms  the  root-systems  differ  remarkably 
in   the   number  of  the   rootlets    and    the   total   length   of  the 
roots.8    In  three  species  the  determinations  of  the  total  length 
were  as  follows  :  — 


1  Haberlandt:  Physiologische  Pflanzenanatomie,  1884,  p.  152. 

2  Hales  gives  as  the  entire  surface  of  these  roots  2, 286  square  inches,  or 
15.8  square  feet  (Vegetable  Statics,  1731,  p.  6). 

3  The  plants  examined  were  grown  from  May  to  October.     Two  of  Nobbe's 
tables  (Die  landwirthschaftlichen  Versuchs-Stationen,  xviii.,  1875,  p.  279)  are 
here  given  :  — 

a.   NUMBER  OF  ROOTLETS. 


Norway  Spruce. 

Silver  Fir. 

Scotch  Pine. 

Boots  of  the  1st  order. 

•    1 

1 

1 

"       "      2d      « 

86 

48 

404 

«        «      jd      it 

162 

85 

1,955 

"        "       4th     " 

5 

0 

749 

"        "      5th     " 

0 

0 

26 

EXTENT    OF   BOOT-SYSTEMS. 


233 


Silver  Fir 1  meter. 

Norway  Spruce 2  meters. 

Scotch  Pine 12  meters. 

All  the  plants  upon  which  these  averages  are  based  were  grown 
under  the  same  conditions. 

627.  When  any  plant 
is  lifted,  even  with  great 
care,  from  the  soil  in 
which  it  has  grown,  many 
of  its  more  delicate  root- 
lets are  torn  off  and  left 
behind.  Hence  it  is 
difficult  to  ascertain  the 
total  amount  of  roots 
belonging  to  a  plant. 
Even  the  best  plan  yet 
devised  for  cleaning  the 
root  previous  to  measur- 
ing it  —  that  of  allow- 
ing a  stream  of  water  to 
wash  awa}-  all  the  earth 
which  it  will  detach  — 
usually  causes  a  few  of 
the  finer  rootlets  to  be 
carried  off.  It  has  been 
shown,  however,  that  the 
roots  of  peas,  beans,  and 
the  common  cereals  are 
abundantly  branched  to 
a  depth  of  more  than  a 
meter,  and  that  many  of 

them  penetrate  considerably  further.     Schubart  states  that  the 
amount,  by  weight,  of  roots  in  peas  and  wheat,  compared  with  that 

b.   LENGTH  IN  MILLIMETERS. 


Norway  Spruce 

Silver  Fir. 

Scotch  Pine. 

Roots  of  the  1st  order. 

290 

300 

873 

"       "     2d     " 

1,333 

636 

4,438 

**        **      3d      ** 

312 

56 

5,491 

«        44      4.th     " 

5 

— 

1,143 

"        "      5th     " 

— 

— 

41 

FIG.  144.  Roots  of  seedlings  of  Triticum  vulgare.  B,  plant  four  weeks  older  than  A. 
The  soil  clings  in  <»ach  case  to  the  younger  parts.    (Sachs.) 


234          ABSORPTION   OF    LIQUIDS   THROUGH    ROOTS. 

of  the  whole  plant  (all  being  dried),  is  less  than  fifty  per  cent.1 
By  comparison  of  the  weights  and  lengths  of  average  pieces  of 
the  roots  of  barley,  it  has  been  found  that  the  whole  root-system 
in  a  vigorous  plant  is  not  far  from  thirty-seven  meters  in  length  ; 
and  that  all  this  could  be  packed  in  a  small  volume  of  fine  soil 
(about  ^  of  a  cubic  foot).2 

628.  The  nature  of  the  soil,  and  especially  the  amount  of 
moisture  and  of  nutritive  matters  which  it  contains,  have  a 
marked  influence  upon  the  development  of  the  root-system  of 
a  plant.  Other  things  being  equal,  fertility  of  the  soil  favors 
compact  branching,  as  is  shown  by  experiments  by  Nobbe.8 

Indian  corn  was  grown  for  a  time  in  several  cylinders  con- 
taining clay  soil ;  then  the  earth  was  carefully  washed  away  and 
the  roots  were  compared.  In  the  first  cylinder  the  soil  had 

1  Amounts  as  given  in  Chemische  Ackersmann,  i.  p.  193. 

Roots  of  winter  wheat  (in  April) 40  per  cent. 

"     peas  (four  weeks  after  planting)    ...     44        " 
"       "     (at  flowering) 24       " 

2  Hellriegel  :  Hoffmann's  Jahresbericht,  1864. 

Nobbe  ( Versuchs-Stationen,  1875,  p.  279)  has  given  some  instructive  figures, 
showing  the  ratio  of  the  surface  above  ground  to  that  below  in  yearling  plants 
of  some  common  species  of  Conifers  grown  under  similar  conditions.  Some  of 
his  figures  are  here  given. 

a.   SURFACE  OF  ROOTLETS. 

Square  millimeters. 

Silver  Fir 2,452. 

Norway  Spruce 4,139. 

Scotch  Pine 20,515. 

b.  SURFACE  OF  THE  GREEN  PARTS  OF  THE  PLANTS. 

Square  millimeters. 

Silver  Fir 1,451. 

Norway  Spruce      . 1,551. 

Scotch  Pine 4,304. 

c.   RATIO  OF  PARTS  IN  THE  PLANTS  EXAMINED. 

Silver  Fir.  Norway  Spruce  Scotch  Pine. 

Parts  above  ground     ...     100  :            107            :            297 

Parts  below  ground     ...     100  :           168            :  .        837 

d.   RATIO  OF  THE  PARTS  ABOVE  GROUND  TO  THOSE  BELOW. 

Silver  Fir 100  :  169 

Norway  Spruce 100  :  267 

Scotch  Pine 100  :  477 

»  Versuchs-Statiouen,  iv.,  1862,  pp.  220,  221. 


DEVELOPMENT    OF   KOOT-SYSTEMS.  235 

been  uniformly  mixed  with  a  fertilizing  substance,  and  in  this 
soil  the  roots  had  developed  in  a  normal  manner.  In  the  sec- 
ond cylinder  a  laj'er  of  the  fertilizing  material  had  been  placed 
three  to  four  centimeters  below  the  surface,  and  in  the  soil  at 
this  plane  the  roots  had  branched  very  abundantly.  In  the 
third  cylinder  a  similar  layer  of  the  fertilizing  matter  had  been 
placed  half-way  down  the  cylinder,  and  here  the  root-branches 
were  far  more  numerous  than  elsewhere.  In  other  cases  the 
fertilizing  substance  had  been  placed  at  the  bottom,  around  the 
sides,  or  in  the  middle  of  the  cylinder,  and  in  these  places  respec- 
tively the  root-branches  were  most  abundant.  Substantially  the 
same  thing  is  observed  in  earth  where  the  roots  of  plants  meet 
with  buried  bones :  the  finer  root-branches  are  developed  around 
and  afterwards  in  the  substance  of  the  decomposing  animal 
matter,  often  forming  dense  mats.1 

629.  In  some  cases  roots  extend  to  very  great  distances ; 
thus  those  of  an  elm  have  been  known  to  till  up  drains  fifty 
yards  distant  from  the  tree.2     It  may  be  said,  in  general,  that 
the  roots  of  the  common  forest  and  shade  trees  reach  to  and  be- 
yond the  eaves  of  the  roof  made  by  the  leafy  branches.    "There 
is  a  constant  relation  between  the  horizontal  extension  of  the 
branches  and  the  lateral  spreading  of  the  roots.     It  is  not  by 
watering  a  tree  close  to  the  trunk  that  it  will  be  kept  in  vigor, 
but  by  applying  the  water  on  the  soil  at  the  part  correspond- 
ing to  the  ends  of  the  branches.     The  rain  which  falls  on  a  tree 
drops  from  the  branches  on  that  part  of  the  soil  which  is  situ- 
ated immediately  above  the  absorbing  fibrils  of  the  roots."  8 

630.  The  root-system  of  a  plant,  ever  extending  by  its  in- 
numerable  subdivisions   into   new  soil,   and   clothed   near  the 
extremities  of  the  rootlets  with  delicate  epidermal  cells,  is  a 
complex  apparatus  for  osmosis  placed  under  the  most  favorable 
conditions  for  absorption. 

631.  The  course  of  the  water  after  it  has  found  its  way  into 
a  plant  through  the  epidermal  cells  of  the  newer  portions  of  the 
roots,  and  the  pressure  which  at  times  the  watery  liquids  in  roots 
exert,  can  be  more  conveniently  examined  at  a  later  stage  (see 
Chapter  IX.,  "  Transfer  of  Water  through  the  Plant "). 

1  See  also  a  paper  by  Detmer  :  Versuchs-Stationen,  1872,  p.  107. 

2  Journal  Royal  Agricultural  Society,  vol.  i.  p.  364,  contains  some  interest- 
ing cases  of  great  length  of  roots. 

8  Balfour  ;  Class  Book  of  Botany,  1854,  p.  427, 


CHAPTER  VIII. 

SOILS,   ASH  CONSTITUENTS,   AND  WATER-CULTURE. 

632.  WHEN  a  plant  is  carefully  dried  at  a  temperature  slightly 
exceeding  that  of  boiling  water  until  it  ceases  to  lose  weight, 
there  remains  behind  a  brittle  combustible  residue.     The  dif- 
ference between  the  weight  of  the  plant  and  that  of  the  resi- 
due represents   the  amount  of  water  previously  contained   in 
the  plant.     This  differs  widely,  according  to  the  kind  of  plant 
and  its  age.     The  following  table  gives  the  proportion  of  water 
contained  in  a  few  of  the  most  common  plants  :  — 

Red  Clover,  before  flowering 83  pe    cent. 

"         "       in  full  flower      .     .     .     .  '.  '.     .  78 

Oats,  before  flowering 82 

"     in  flower 77 

Turnip  (root) 91 

Beech  (leaves),  in  summer 75 

"  "        in  autumn 55 

Dry  grains 14  to  15 

Dry  woods 15 

633.  If  the  brittle  residue  left  after  complete  expulsion  of  the 
water  is  burned  in  the  open  air,  there  remains  behind  a  small 
amount  of  gray  ash ;   all  the  rest  is  wholly  consumed.     The 
amount  of  ash  also  varies  widely,  according  to  the  kind  of  plant 
and  its  age.     In  the  following  table 1  are  given  the  proportions 
for  a  few  common  plants  :  — 

Per  cent  of  ash  in  Per  cent  of  ash  in 

fresh  material.  dry  material. 

Red  Clover 1.5  5.6 

Sugar  Beet  (root) 8  4.3 

Indian  Corn 1.1  5.5 

"     (grain) 2.1  1.5 

Beech  (leaves),  in  summer    ...         1.3 
"          "         in  autumn     ...        3. 

634.  In  a  general  way  it  ma}r  be  said  that  the  combustible 
matters  are  derived  chiefly  from  the  atmosphere,  while  all  the 

1  The  student  is  referred,  for  detailed  accounts  of  analyses  from  which  these 
figures  have  been  chiefly  taken,  to  Johnson's  "How  Crops  Grow,"  1868. 


FORMATION   OF  SOILS.  237 

water  and  the  incombustible  ash  come  from  the  soil.  In  the  case 
of  aquatics  this  general  statement  would  not  appear  to  hold,  for 
they  obtain  all  their  substance  from  the  water  in  which  they  live  ; 
but,  as  will  be  seen  later,  this  source  is  essentially  the  same. 
We  have  examined  in  the  previous  chapter  one  of  the  means 
by  which  plants  obtain  their  supply  of  water  and  ash  materials, 
and  it  will  be  best  to  consider  now  the  source  from  which  this 
supply  comes,  before  approaching  the  study  of  the  combustible 
substance  of  plants. 

SOILS. 

635.  Formation  of  soils.     Soils  are  produced  b}-  the  disinte- 
gration of  rocks.     This  may  be  mechanical,  as  that  caused  by 
crushing,  attrition,  and  the  action  of  frost ;  or  it  may  be  and 
generally  is  associated  with  more  or  less  chemical  change.     In 
soils,  some  of  the  products  of  the  decomposition  of  organic  sub- 
stances are  usuall}'  intermingled  with  purely  mineral  matters 
aggregated  in  various  degrees  of  fineness.      Soils  exposed  to 
atmospheric  influences  constant!}-  change  both  in  their  physical 
properties  and  chemical  composition,  the  changes  being  brought 
about  chiefly  by  the  combined  action  of  moisture,  carbonic  acid, 
and  oxygen. 

636.  Water  not  only  wears  away  solid  rocks  by  its  mechanical 
action,  but  after  it  has  insinuated  itself  into  the  crevices  of 
rocks  it  accomplishes  the  work  of  disintegration  far  more  rapidly 
by  its  expansion  during  freezing.1 

When  rocks  become  loosened  b}*  running  water,  or  by  the 
slow  movement  of  glaciers,  the  crushing  and  grinding  of  the 
pieces  which  come  into  contact  are  sufficient  to  pulverize 
the  hardest  of  the  more  common  ones. 

Water,  especially  when  it  holds  carbonic  acid  in  solution,  is 
a  very  important  agent  in  changing  the  characters  of  rocks ; 
sometimes  it  does  this  by  dissolving  out  portions  of  the  rocks, 
sometimes  by  bringing  about  new  combinations  of  their  con- 
stituents. Moreover,  rain-water  contains  a  minute  quantity  of 
other  matters  besides  carbonic  acid,  and  these  exert  a  powerful 
effect  in  disintegrating  and  dissolving  certain  rocks. 

637.  The  free  oxygen  of  the  atmosphere  is  also  an  efficient 
agent  in  the  changes  by  which  rocks  are  broken  down  to  form 

1  The  amount  of  expansion  is  usually  given  as  approximately  one  fifteenth 
of  the  volume. 


238  SOILS. 

soils.  Many  rocks  contain  ferrous  oxide,  which  readily  under- 
goes further  oxidation  ;  certain  sulphides  in  rocks  are  oxidizable 
under  the  ordinary  conditions  found  in  a  moist  atmosphere,  and 
in  such  cases  the  chemical  action  results  in  rendering  the  rocks 
brittle. 

638.  Water  can  easily  transport  the  finer  particles  of  soil 
from  where  they  were  formed  by  disintegration  of  the  rocks  to 
points  at  distances  from  their  source,  varying  with  their  weight. 
For  this  reason  the  particles  accumulate  in  different  degrees 
of  fineness  at  different  points  along  water-courses. 

639.  It  is  believed  that  during  the  Glacial  period,  when  large 
portions  of  the  northern  hemisphere  were  covered  deeply  with 
sheets   of  moving   ice,    immense   amounts   of  coarse   and  fine 
soils  were  carried  far  from  the  places  where  they  were  formed, 
and  were  heaped  up  more  or  less  irregularly  in  the  masses  which 
now  form  gravelly  hills  and  ridges.      The  glacial  action  now 
going  on  in  the  Alps  shows  how  vast  must  have  been  the  soil- 
making  and  soil-carrying  power  of  the  glaciers  which  once  cov- 
ered so  much  of  our  continent. 

640.  Soils  which  have  not  been  carried  by  water  or  ice  from 
the  place  where  they  were  formed  by  some  of  the  agencies  men- 
tioned above  are  not  generally  of  great  depth,  and  their  nature 
can   usually  be   made   out  by  examination  of  the   contiguous 
rocks. 

641.  Classification  of  soils.      For  our  present  purpose  soils 
may  be  classified  as  gravelly,  sand}-,  clayey,  calcareous,  loamy, 
and  peaty.      Gravelly  soils  differ  widely  in  their  chemical  char- 
acter, since  the  pebbles  which  compose  them  may  be  either  chiefly 
quartz  and  fragments  of  rocks  in  which  quartz  predominates,  or 
there  may  be  also  a  good  proportion  of  limestone,  or  of  feld- 
spathic   rocks.      With   the   coarse   pebbles    is    intermingled   a 
certain  proportion  of  finer  soil.     Sandy  soils  are  usually  made 
up  of  fine  quartz   with  which  some   other   matters   are   asso- 
ciated, such  as  some  compound  of  iron,  grains  of  feldspathic 
minerals,  micaceous  particles,  etc.     In  a  few  cases,  however, 
the  sandy  soils   differ  widely  from   this   composition ;    for  in- 
stance, the  green  sand  of  New  Jersey  contains  a  large  proportion 
(more  than  fifty  per  cent)  of  green  grains  of  a  silicate  of  iron  and 
potassium.      Clayey  soils  are  generally  derived  from  the  dis- 
integration of  various  feldspathic  rocks,  and  are  mixtures  of 
hydrated  aluminic  silicate  with  many  other  matters.     Such  soils 
are  generally  adhesive,   are  retentive  of  water,   and  dry  into 
a  hard  mass ;    these  characters  which  belong  to  true  clay  art- 


PHYSICAL   PEOPERTIES   OP   SOILS.  239 

found  also  in  some  soils  which  are  not  clays,  and  hence  the 
term  clayey  is  sometimes  loosely  applied.  Calcareous  or  lime 
soils  contain  calcic  carbonate  in  large  amount.  To  calcareous 
clay,  when  the  ingredients  are  in  a  state  of  rather  fine  subdi- 
vision, the  name  marl  is  frequently  applied.  Peaty  or  humus 
soils  are  those  which  contain  a  considerable  proportion  of  par- 
tially decayed  vegetable  matter  ;  when  such  matter  decays  under 
water  it  becomes  peat,  or  muck ;  when  it  decays  without  much 
water  it  is  generalh7  known  as  mould. 

642.  By  mechanical  analysis,  as  by  simple  washing  and  sift- 
ing, it  is  possible  to  separate  a  soil  into  its  mechanical  ingre- 
dients, which  are:  (1)  Gravel;  (2)  coarse  sand;  (3)  fine  sand; 
(4)  clayey  sand  ;   (5)  clayey  substance,  or  fine  clay. 

The  mechanical  subdivision  of  soils  has  an  important  bearing 
upon  their  physical  properties  and  upon  their  adaptability  to 
the  growth  of  roots  and  the  sustenance  of  plants.1 

From  interesting  studies  by  Darwin,2  it  is  plain  that  in  some 
localities  earth-worms  have  exerted,  by  their  burrowing  and 
tunnelling,  a  vast  influence  in  changing  the  physical  character 
of  the  soils  in  which  they  thrive. 

643.  Physical  properties  of  soils.    Of  these,  the  most  important 
to  be  considered  here  are  those  which  affect  the  relations  of  soils 
to  liquids,  to  gases,  and  to  heat ;  for  all  of  these  directly  affect 
the  growth  and  indirectly  the  nutrition  of  plants. 

644.  Absorption  and  retention  of  moisture  by  soils.     It  is  con- 
venient to  examine  the  relations  of  soils  both  to  liquid  water 
and  to  aqueous  vapor.     Soils  can  absorb  from  the  atmosphere 
and  condense  upon  the  surface  of  their  particles,  or  in  their  inter- 
stices, a  certain  amount  of  the  vapor  of  water.     This  property 
of  absorption,  known  as  that  of  hygroscopicity,  is  different  in 
different  soils,  as  shown  by  the  following  table  from  Schiibeler.3 

Five  hundred  centigrams  of  each  soil  carefully  dried  were 
spread  over  a  surface  of  thirty-six  thousand  square  millimeters, 
and  exposed  for  varying  periods  to  an  atmosphere  saturated 
with  watery  vapor ;  the  amounts  of  waters  absorbed  (in  centi- 
grams) were  as  follows  :  — 

1  The  reader  should  examine  a  paper  by  J.  D.  Whitney  (Plain,  Prairie,  and 
Forest),  in  which  is  discussed  the  probable  influence  of  the  extreme  fineness  of 
prairie  soils  upon  the  absence  of  forests.     See  American  Naturalist,  October 
and  November,  1876. 

2  Darwin  :  The  Formation   of  Vegetable  Mould   through   the  Action  of 
Worms. 

8  Knop's  Lehrbuch  der  Agricultur-Chemie,  1868,  vol.  ii.  pp.  13,  14. 


240 


SOILS. 


12  hours. 

24  hours. 

48  hours. 

72  hours. 

Quartz  sand  .     . 

0.0 

0.0 

0.0 

0.0 

Calcareous  saud 

1.0 

1.5 

1.5 

1.5 

Clayey  soils  .     . 

10.5  to  15. 

13  to  18. 

14  to  20. 

14  to  20.5 

Clay    .... 

18.5 

21.0 

24.0 

24.5 

Garden  earth     . 

17.5 

22.5 

25.0 

26.0 

Humus     .     .     . 

40.0 

48.5 

55.0 

60.0 

From  these  figures  it  appears  (1)  that  the  greater  part  of  the 
vapor  is  condensed  before  the  expiration  of  a  single  da}',  (2)  that 
humus  is  by  far  the  most  hygroscopic,  but  (3)  that  clay  can  ab- 
sorb a  large  quantity  of  vapor. 

Temperature  exerts  a  marked  influence  upon  the  capacity  of 
soils  to  absorb  aqueous  vapor,  as  is  shown  by  Knop's  exami- 
nation l  of  a  sandy  and  of  a  rich  earth ;  the  amount  of  vapor 
absorbed  diminishes  with  elevation  of  temperature. 

645.  The  amount  of  liquid  water  which  soils  can  absorb  and  re- 
tain is  very  different  for  different  kinds  of  earth.  In  the  follow- 
ing determinations  by  Schubeler  dry  soils  were  saturated  with 
water  upon  a  funnel,  and  the  increase  of  weight  was  noted  after 
all  the  excess  of  water  had  dripped  away.  The  first  column  gives 
the  percentage  of  increase  in  weight  of  soil ;  the  second,  the  num- 
ber of  volumes  of  water  that  one  hundred  volumes  of  soil  can  take 
up  ;  the  third,  the  percentage  of  this  water  which  evaporates  from 
the  soil  in  four  hours  when  it  is  spread  over  a  given  surface.2 


1. 

2. 

3. 

25 

37.9 

88.4 

Calcareous  sand     .... 
Clay  soil  (60%  clay)       .     . 
Clay  soil  (76%  clay)       .     . 
Heavy  clay  (89%  clay)   .     . 
Pure  clay     
Hum  us  8 

29 
40 
50 
61 
70 
190 

44.1 
51.4 
57.3 
62.9 
66.2 
69  2 

75.9 
52 

34.9 
31.9 
25  5 

646.   The  degree  of  fineness  exerts  also  some  influence  upon 
the  absorptive   power;    but  while  pulverization  increases  that 

1  Versuchs-Stationen,  vi.,  1864,  p.  281,  where  are  found  also  some  interesting 
results  recorded  by  Knop,  in  regard  to  the  absorption  of  aqueous  vapor  by 
various  organic  substances. 

2  Knop's  Lehrbuch,  1868,  vol.  ii.  p.  26.     The  third  column  is  cited  from 
Johnson's  "How  Crops  Feed,"  1870,  p.  180. 

3  Samples  of  peat  have  been  known  to  absorb  from  300  to  more  than  500 
per  cent  of  water. 


ABSORPTION   OF  MOISTURE  BY  SOILS.  241 

power  in  some  kinds  of  soil  it  diminishes  it  in  others.  Thus 
Zenger  has  shown  that  fine  quartz  sand  absorbs  about  twice  as 
much  water  as  that  which  is  coarse;  on  the  other  hand,  fine 
brick-clay  is  not  so  absorbent  as  coarse. 

647.  Admixture  of  heterogeneous  matters  with  soil  generally 
lowers  the  absorptive  and  retentive  power  both  of  the  soil  and  of 
the  added  substances.  Treutler  examined  certain  soil  mixtures 
in  the  following  manner :  fifty  grams  of  the  soil  were  placed  in 
one  hundred  cubic  centimeters  of  water  for  twenty-four  hours, 
the  excess  of  water  was  allowed  to  drip  away,  and  the  amount 
then  retained  noted.  The  following  are  among  his  results :  — 


Soils. 

Cubic  centime- 
ters of  water 
retained. 

Mixtures. 

Cubic  centime- 
ters of  water 
retained. 

Fine  earth 
Quartz  sand 
Caustic  lime 
Bone-dust 

34.2 

14. 
61. 
46. 

40  grm.  fine  earth  and  10  grm.  caustic  lime 
40  gnn.  quartz  sand  and  10  grm.  caustic  lime 
40  grm.  quartz  sand  and  10  grm.  bone-dust 
30  grm.  quartz  sand  and  20  grm.  bone-dust 

44. 
19. 
16.5 
9. 

From  Treutler's  tables  it  appears  that  the  absorptive  and 
retentive  capacity  of  a  mixture  of  two  substances  may  equal 
that  of  the  constituents,  but  that  generally  it  becomes  lower. 

648.  A  soil  may  be  so  fine  and  compact  that  rain  will  not 
readily  penetrate  it ;    or  on  the  other  hand  it  may  be  so  porous 
as  to  allow  the  water  which  falls  on  it  to  pass  rapidly  down 
through  it.     A  soil  of  proper  texture  will  receive  the  rains,  and, 
as  has  been  shown  by  the  foregoing  paragraphs,  retain  a  certain 
amount  in  its  pores,  the  excess  draining  away. 

649.  Evaporation  of  water  goes  on  continually  from  the  sur- 
face of  moist  soil,  unless  the  atmosphere  is  saturated,  and  the 
amount  of  evaporation  depends   largely  upon   the  amount  of 
moisture  present  in  the  state  of  vapor  in  the  atmosphere  at  any 
given  time.     But  the  retentive  power  spoken  of  above  (which 
is  plainly  opposed  to  evaporation)  is  very  different  in  different 
soils  ;  for  this  reason  about  three  times  as  much  water  evaporates 
from  quartz  sand  as  from  the  same  amount  of  humus  equally 
exposed  for  a  given  time.     When  by  evaporation  the  soil  be- 
comes dry  at  the  surface,  a  draft  is  made  upon  the  supply  of 
water  retained  in  it  at  a  greater  depth,  and  this  water  then  rises 

y  capillarity  to  the  drier  layers.     It  is  therefore  said  that  there 
?  n  constant  movement  of  water  in  the  soil. 
16 


242  SOILS. 

650.  A  distinction  may  be  property  made  between  (1)  that 
water  which  remains  as  a  copious  supply  beneath  the  surface  of 
the  ground,  existing  there  plainly  as  a  liquid,  (2)  that  which  ad- 
heres to  the  particles  of  soil  imparting  to  them  a  moist  appear- 
ance, (3)  that  which  adheres  to  the  particles  of  an  air-dry  soil 
and  which  does  not  affect  at  all  the  appearance  of  the  particles. 
The  first  has  been  called  hydrostatic,  the  second,  capillary,  the 
third,  hygroscopic  water.     It  is  from  the  two  latter  that  the 
roots  of  plants  other  than  aquatics  usually  obtain  their  supply 
of  moisture.1 

651.  The  relations  which  evaporation  and  drainage  bear  to 
the  total  rain-fall  upon  the  soil  have  been  examined  during  a 
series  of  nineteen  years  at  Rothamsted,  in  England.     The  fol- 
lowing figures  are  based  on  the  results  during  ten  years  (Sep- 
tember, 1870,  to  August,  1880). 

Rain-fall 30.68  inches, 

Drainage  from  soil 

at  20  inches  depth 13.21      " 

at  40     "         " 13.94      " 

at  60     "        " 12.17      " 

Amount  of  water  retained  by  soil,  or  evaporated 

at  20  inches  depth 17.47      " 

at  40     "         " 16.74      " 

at  60     "        " 18.51      " 

Percentage  of  rain-fall  lost  by  drainage 

at  20  inches  depth 43.1 

at  40     "         " 45.4        " 

at  60     "         " 39.7 

Percentage  of  rain-fall  retained  by  soil,  or  lost  by  evaporation 

at  20  inches  depth 56.9        " 

at  40     "         " 54.6        " 

at  60     "         " 60.3        " 

652.  Soils  are  not  only  acted  upon  by  the  solvent  power  of 
water,  as  shown  in  636,  but  many  soils  possess  the  remarkable 
property  of  removing  saline  matters  from  aqueous  solutions. 

The  interesting  fact  that  impure  water  can  be  freed  from  some 
of  its  foreign  matter  1)3*  being  filtered  through  earth  has  long 
been  known,  but  its  significance  in  the  nutrition  of  plants  does 
not  appear  to  have  received  attention  until  1819.  Gazzeri2at 

1  For  a  full  discussion  of  this  subject,  which  is  most  important  in  its  bear- 
ings upon  the  cultivation  of  plants,  the  student  should  study  Johnson's  "  How 
Crops  Feed,"  p.  199. 

2  From  a  note  by  Orth :  Versuchs-Stationcn,  xvi.,  1873,  p.  57.    The  discovery 
is  generally  ascribed  to  Rronner,  1836.     The  fullest  treatment  was  by  Way  : 
Journal  Royal  Agricultural  Society,  1850,  and  later. 


CHEMICAL    ABSORPTION    BY   SOILS.  243 

that  date  says:  "Earth,  especially  clay,  seizes  upon  the  sol- 
uble matters  intrusted  to  it,  and  holds  them  back,  in  order 
that  it  may  gradually  furnish  them  to  plants  according  to  their 
needs." 

653.  When  dilute  solutions  of  a  salt  are  slowly  filtered  through 
sand  which  contains  a  good  admixture  of  clay,  the  water  passes 
out  for  a  time  without  more  than  a  trace  of  the  salt,  and  in 
some  cases  all  the  salt  is  retained  by  the  soil.     Even  sewage 
liquids  can  by  this  method  be  freed  from  their  offensive  ingre- 
dients.    This  phenomenon  of  filtration  is  due  to  adhesion  (that 
is,  the  attraction  which  the  surface  of  one  kind  of  matter  has 
for  another  kind  of  matter).    The  substances  which  are  removed 
by  the  particles  of  soil   are  so  fastened  to  them  that  even 
when  the  soil  is  washed  in  pure  water  onhr  traces  of  them  are 
removed. 

654.  Chemical  absorption  by  soils.     Besides  this  physical  ad- 
hesion, there  are  exhibited  by  many  soils  certain  chemical  phe- 
nomena also,  which  have  been   collectively   termed  chemical 
absorption.     If  a  solution  of  potassic  nitrate  is  filtered  through 
a  well-pulverized  clay  soil  containing  an  admixture  of  insoluble 
compounds  of  magnesium  and  calcium,  such  as  are  met  with  in 
almost  an}*  ordinary  soil,  the  water  which  drains  off  will  con- 
tain very  little  if  indeed  an}-  potassium ;  but  it  will  have,  in- 
stead, magnesium  and  calcic  nitrate  in  appreciable  amount.   But 
this   absorptive   power  of  a  soil  is  soon   satisfied ;    for  after 
a  certain  amount  of  potassium  has  been  removed  no  more  is 
taken  up. 

The  strength  of  the  saline  solution  affects  the  amount  of 
absorption,  more  of  the  base  being  absorbed  from  strong  solu- 
tions. Different  substances  are  absorbed  by  the  soil  in  different 
amounts ;  thus  in  the  experiments  by  Peters  the  bases  were 
absorbed  in  the  following  order:  (1)  Potassa,  (2)  Ammonia, 
(3)  Soda,  (4)  Magnesia,  (5)  Lime.  Different  soils  absorb  the 
same  substance  in  different  amounts,  depending  upon  the  physi- 
cal condition  of  the  soil,  but  chiefly,  it  is  believed,  upon  the 
mode  in  which  the  substance  is  combined  ;  thus,  more  potassa  is 
absorbed  from  the  phosphate  than  from  the  carbonate,  and  more 
from  the  latter  than  from  the  sulphate. 

In  general  it  may  be  said  that  the  salts  of  the  alkalies  and 
the  alkaline  earths  are  so  absorbed  by  rich  soils  that  the  bases 
are  retained  in  new  combinations,  while  the  acids  pass  off, 
having  also,  of  course,  formed  new  combinations.  The  phos- 
phates and  silicates  are  retained  undecomposed.  The  case  of 


244  SOILS. 

the  latter  compounds  may  be  regarded  as  the  ordinary  physi- 
cal absorption,  that  of  the  former  as  the  so-called  chemical 
absorption. 

655.  The  matters  absorbed  b}*  the  soil  may  be  released  after 
a  time  and  pass  into  solution  again,  or  they  ma}'  be  displaced 
from  the  soil-particles  by  the  filtration  of  new  solutions.     When 
it  is  remembered  that  rain-water  exerts  a  powerful  solvent  action 
upon  some  portions  of  the  soil,  and  that,  on  the  other  hand, 
the  soil  can  remove  from  aqueous  solutions  some  of  the  matters 
therein  dissolved,  the  complicated  nature  of  the  problem  which 
presents  itself  is  at  once  apparent.     Examination  of  the  waters 
which  drain  through  soil,  and  which  may  fairly  represent  the 
resultant  of  the  solvent  action  of  the  water  and  the  absorptive 
power  of  the  soil,  shows  that  from  thirteen  to  fifty  parts  of  solid 
matters  may  remain  dissolved  in  100,000  parts  of  water.     (The 
question  of  nitrogen  compounds  in  drainage-water  will  be  ex- 
amined in  a  subsequent  chapter.) 

656.  Condensation  of  gases  by  soils.     Soils  have  the  power  of 
condensing  in  their  pores  certain  amounts  of  different  gases. 
These  condensed  gases  are  released  when  the  soils  are  subjected 
to  a  high  temperature,  say  140°  C.,  and  their  amounts  can  then 
be  measured.      The  figures  below  give  the  results  of  the  meas- 
urements in  several  instances,  100  grains  of  soil  being  taken 
in  each  case. 

Soil.  Cubic  centimeters  of  gas  yielded. 

Peat 162 

Clay 30 

Moist  garden  soil 14 

It  is  found  that  in  the  soil  there  is  present  a  smaller  amount 
of  oxygen  and  a  larger  amount  of  nitrogen  than  in  the  atmos- 
phere. The  percentage  of  carbonic  acid  in  the  soil  is  also  some- 
what larger  than  that  in  the  atmosphere ;  especially  in  soils 
which  contain  much  organic  matter. 

657.  Root- absorption  of  saline  matters  from  soils.    Having  seen 
that  the  soil,  the  principal  medium  in  which  roots  extend,  pos- 
sesses the  power  of  absorbing  and  retaining  water,  saline  mat- 
ters, and  gases,  attention  must  next  be  directed  to  the  conditions 
under  which  the  root-hairs  can  abstract  from   it  the   matters 
requisite  for  the  plant.    These  conditions  are  (1)  presence  of  free 
oxygen,  (2)  a  certain  temperature,  (3)  the  presence  of  saline 
matters  in  an  available  form  in  the  soil. 

658.  Free  oxygen  is  necessary  to  all  protoplasmic  activity, 


SOIL  TEMPERATURES.  245 

and  the  plant  will  speedily  show  when  the  amount  required  for 
the  absorptive  activity  of  its  roots  is  not  furnished.  Different 
plants,  however,  require  different  amounts :  thus  aquatics  and 
marsh-plants  do  not  need  so  much  oxygen  for  their  roots  as 
do  plants  which  ordinarily  grow  in  a  porous  soil.  Partial  ex- 
clusion of  oxygen  from  the  roots  of  the  latter  by  keeping  the 
soil  saturated  with  water  usually  injures  the  plants  in  a  short 
time. 

It  has  been  shown  by  Sachs  and  others  that  seedlings  of  many 
plants  normally  growing  in  dryish  soil  will  develop  if  treated  as 
aquatics  ;  better  results  are  obtained,  however,  if  air  is  occasion- 
ally passed  through  the  water. 

659.  The  temperature  needed  for  the  absorptive  activity  of 
roots  varies  with  different  plants.     It  may  be  said,  however, 
that  for  any  given  plant  the  absorptive  power  increases  with 
increase  of  temperature. 

660.  Different  soils  have  very  different  relations  to  temper- 
ature.     Leaving  out  of  account  the  small  amount  of  warmth 
derived  from  the  chemical  changes  going  on  in  the  soil  by  which 
heat  is  evolved,  it  may  be  said  that  the  heat  of  the  soil  is  derived 
from  the  sun's  rays.     The  angle  at  which  these  rays  strike  the 
soil  must  have  a  great  influence  upon  its  temperature.     Again, 
there  are  various  local  causes,  such  as  protecting  or  reflecting 
walls,  which  may  considerably  modify  the  temperature  in  any 
given  case.     The  soil  itself  exerts  a  marked  influence  upon  the 
amount  of  heat  which  it  can  receive  and  retain.     Dark  soils  ab- 
sorb heat  most  readily ;  but  it  has  been  shown  that  black  soils 
are  less  absorbent  of  heat-rays  than  are  those  which  are*  dark 
gray.     The  radiating  power  of  a  soil  depends  upon  the  character 
of  its  surface,  being  much  greater  in  the  case  of  fine  mould  than 
in  that  of  coarse,  gravelly  soils. 

661.  It  must  be  noted,  however,  that  the  heat-rays  which  fall 
upon  a  given  soil  ma}-  have  different  degrees  of  intensity.     Some 
bodies  (e.  g.  lampblack),  can  absorb  and  give  off  b}-  radiation 
heat  of  high  as  well  as  that  of  low  intensity ;  while  other  bodies 
(e.  g.  snow),  absorb  heat  of  low  intensity  only.     Heat  of  high 
intensity  is  converted  into  that  of  low  intensity  by  the  interpo- 
sition of  a  black  covering  of  an}-  kind  which  can  absorb  it  and 
give  it  out  below  as  heat  of  low  intensity. 

662.  At  the  depth  of  fifty  feet  the  temperature  of  the  soil  in 
the  temperate  zone  varies  within  the  limits  of  one  degree,  and 
at  a  depth  somewhat  below  this  it  is  constant.     The  stationary 
temperature  at  such  a  depth  is  the  same  as  that  of  the  mean 


246  ASH  CONSTITUENTS  OF  PLANTS. 

annual  temperature  of  the  atmosphere  in  temperate  regions.1 
Moisture  exerts  a  very  great  effect  in  equalizing  the  capacities 
of  different  soils  for  absorbing  and  retaining  heat. 

663.  That  the  saline  matters  in  the  soil  must  be  in  a  form  in 
which  the  plant  can  make  use  of  them,  appears  from  what  has 
been  said  about  osmosis.     It  should  be  specialty  noticed,  how- 
ever, that  younger  roots  may  exert  a  solvent  action  upon  soil- 
particles. 

Root-hairs,  as  Sachs2  has  shown,  evolve  small  amounts  of 
acid,  which  exert  a  distinctly  corrosive  effect  upon  certain  min- 
eral matters  with  which  they  come  in  contact.  Hence  there  is  a 
continual  unlocking  of  the  nutritive  mineral  materials  fastened  in 
the  soil ;  the  release  being  at  the  very  points  where  the  root-hairs 
are  present  to  absorb  them. 

ASH  CONSTITUENTS  OF  PLANTS. 

664.  These  occur  in  all  parts  of  plants.     It  has  been  shown 
(p.  39)  how  frequently  cell-walls  are  impregnated  or  incrusted 
by  mineral  matters,  which  after  careful  calcination  may  be  left 
as  a  distinct  skeleton  of  the  tissues  of  which  they  formed  a  part. 
But  the  matters  within  cells,  both  the  protoplasmic  substance  and 
the  cell-sap,  also  contain  a  certain  amount  of  incombustible  ma- 
terial.    The  total  amount  of  ash  constituents  varies  greatly  in 
different  plants,  in  different  parts  of  the  same  plant,  and  also 

1  Pe^ihallow,  Soil  Temperatures  (Hough ton  Farm  Experiment  Department), 
1884.     See  also  Knop,  Agricultur-Chemie,  i.,  1868,  p.  469. 

2  Moldenhawer  (Beytrage),  in  1812,  expressed  the  view  that  roots  probably 
set  free  certain  matters  which  can  unloose  nutritive  materials.     De  Candolle 
( Physiologic,  1832)  described  the  corrosive  action  of  lichens  on  underlying 
rocks  ;  and  Liebig,  in  1839,  studied  the  action  of  roots  on  the  color  of  litmus 
solutions. 

Sachs's  experiment  (1860)  is  well  adapted  to  class  demonstration.  A  pol- 
ished plate  of  marble  is  covered  with  moist  saw-dust,  and  in  this  a  few  seeds  are 
planted.  After  the  seedlings  have  grown  for  a  time  the  saw-dust  is  removed, 
when  the  marks  left  upon  the  stone  by  the  corroding  rootlets  can  be  plainly 
seen.  If  the  corroded  marble  is  rubbed  slightly  with  a  little  vermilion,  the 
traces  made  by  the  root-hairs  will  be  very  distinct.  In  the  early  publication 
of  Sachs,  the  secretion  by  which  the  corrosion  is  effected  was  said  to  be  car- 
bonic acid  ;  but  he  does  not  appear  to  hold  this  view  now.  Whether  the  action 
is  due  to  acetic  acid,  as  Oudemann  and  Kauwenhoff'  suggest,  or  to  different 
acids  varying  with  plants  or  times,  as  intimated  by  Pfeffer,  it  is  certainly 
highly  corrosive  in  some  cases.  In  an  experiment  by  Schulz,  the  rootlets  of 
germinating  Leguminosae  and  Graminese  exhibited  a  faint  alkaline  reaction 
(Journal  fair  Praktische  Chemie,  Ixxxvii.,  1862,  p.  135). 


COMPOSITION   OF   THE   ASH.  247 

in  many  cases  with  the  age  of  the  plant.    The  following  table 1 
indicates  the  per  cent  of  ash  in  a  few  instances  :  — 

Turnip  (fresh) 7 

Sugar  beet  (fresh) 8 

Potatoes  (fresh) 9 

Red  clover  (fresh) 1.3 

Red  clover  (dry) 5.6 

Birch-wood  (dry) 2 

Apple-tree  wood  (dry) 1.1 

Walnut-wood  (dry) 2.5 

Birch-bark 1.1 

Mulberry  leaves  (fresh) 1.1 

Horse-chestnut  leaves  (spring) 2.1 

Horse-chestnut  leaves  (autumn) 3.0 

Apples  (fresh) 3 

Pears  (fresh) 4 

Flax-seed 3.2 

Clover-seed 3.6 

Hemp-seed 4.8 

Beech-nuts 2.7 

Wheat-grains 1.7 

Hemp  (entire  plant) 2.8 

665.  Composition  of  the  ash  of  plants.  Examination  of  trust- 
worth}1  analyses  of  the  ash  of  flowering  plants  shows  that  certain 
elements  are  always  present  in  it.  These  are  potassium,  calcium, 
magnesium,  and  phosphorus.  Besides  these,  which  always  ap- 
pear in  appreciable  amount,  there  are  others  which  are  nearly 
or  quite  as  constant  in  occurrence,  although  in  some  reports  of 
analyses  they  are  not  given,  because  existing  in  such  small  pro- 
portion. They  are  iron,  chlorine,  sulphur,  and  sodium.  The 
elements  mentioned  are  usually  recorded  in  analyses  in  the  fol- 
lowing combinations :  potassa,  phosphoric  acid,  lime,  magnesia, 
sulphuric  acid,  soda,  and  ferric  oxide.  But  it  is  to  be  observed 
that  the  combinations  stated  in  the  tabulation  of  analyses  are  by 
no  means  designed  to  exhibit  all  those  in  which  the  elements 
occur  in  the  plant ;  for  instance,  the  sodium  and  potassium  are 
presumably  combined  with  the  chlorine.  Again,  it  must  be  no- 
ticed that  upon  combustion  the  mineral  matters  in  the  plant  are 
commingled  with  a  larger  or  smaller  amount  of  carbonates,  the 

1  E.  Wolff,  Die  Mittlere  Zusammensetzung  der  Asche,  1865,  p.  77  et  seq. 
See  also  an  excellent  revised  translation  of  Wolff's  tables  in  the  Appendix  of 
Johnson's  "How  Crops  Grow"  (1868).  For  the  percentage  of  ash  in  trees 
and  woody  plants,  as  well  as  the  amounts  of  phosphoric  acid  and  potash  found 
in  such  ash,  see  a  very  valuable  table  by  Storer  (Bulletin  Bussey  Institution, 
1874,  pp.  207-245). 


248 


WATER-CULTUKB. 


amount  depending  somewhat  "upon  the  temperature  at  which 
the  ash  is  prepared."  In  the  following  short  table  a  few  of  the 
many  analyses  collated  by  Johnson *  have  been  brought  together 
to  exhibit  the  proportions  of  the  ash  constituents. 


Name  of  plant. 

J- 

Us. 

I 

1 

1 

•g 

II 

* 

o 

1 

c5 

| 

s 

6 

fi 

i 

i 

1 

<3 

Root  of  sugar  beet  . 

48. 

14.4 

6.4 

9.5 

4.7 

10.4 

1. 

3.8 

2.3 

Potato  tubers     .     . 

60.9 

18.3 

2.4 

4.6 

7. 

1.7 

.9 

1.9 

2.7 

Stalks  of  Indian  corn 

36.3 

8.3 

10.8 

5.7 

5.2 

1.25 

2.4 

28.8 

Wheat-grain       .     . 

31.3 

46.1 

3.2 

12.3 

3.2 

1.9 

666.  The  foregoing  table  indicates  that  wide  diversity  exists 
in  the  amounts  of  the  ordinary  ash  constituents  of  common 
plants.     But  comparison  of  a  large  number  of  analyses  shows 
that  the  following  general  statements  may  be  made :  — 

1.  Plants  which   closely  resemble  each  other  in   structural 
characters  have  substantially  the  same  proportions  of  ash  con- 
stituents. 

2.  The  proportions  of  the  ash  constituents  in  any  part  of  a 
plant  may  vary  within  certain  limits  ;  and  these  limits  may  differ 
at  different  periods  of  growth. 

3.  The  proportions  may  vary  widely  for  different  parts  of  the 
same  plant. 

667.  Not  only  are  the  elements  enumerated  in  the  first  list  in 
665  always  present  in  the  ash  of  flowering  plants,  but  they  are 
shown  by  experiment  to  be  indispensable  to  their  full  develop- 
ment; and  there  is  a  reasonable  certainty  that  iron,  sulphur, 
and  probably  chlorine,  should  be  placed  in  the  same  category  of 
indispensable  elements. 

According  to  Nageli,2  some  of  the  flowerless  plants,  notably 
the  moulds  and  the  schizomycetes,  can  attain  full  development 
with  fewer  elements. 

WATER-CULTURE. 

668.  Apparatus.   While  chemical  analysis  of  the  ash  of  plants 
reveals  the  character  of  the  mineral  matters  which  the}'  absorb 
from  water  and  soil,  it  cannot  materially  aid  the  investigator  in 


1  How  Crops  Grow,  1868,  p.  150. 

8  Sitzungsb.  d.  bayer.  Akad.,  1879,  p.  34Q. 


APPARATUS. 


249 


learning  the  office  of  each  constituent.  This  is  more  satisfac- 
torily accomplished  by  water-culture,  which,  reduced  to  its  sim- 
plest terms,  consists  in  furnishing  to  the  plant  under  proper 
conditions  different  mineral  matters  in  aqueous  solution,  and 
noting  their  effects  upon  it.  It  has  been  long  known  that  plants 
can  be  grown  to  a  considerable  size  in  ordinary  river-water,  or 
water  holding  in  solution  certain  mineral  salts.1  But  it  was  not 
until  1858  that  the  method  of  water-culture  was  systematically 
applied  by  Sachs,  Knop,  and  Nobbe  to  the  investigation  of  the 
relative  value  and  the  office  of  the  different  mineral  constituents 
in  the  nutrition  of  plants.  It  has  since  been  widely  employed  in 
the  examination  both  of  flowering  and  flowerless  plants. 

669.  The  method  adopted  for  ordinary  flowering  plants  is  es- 
sentially as  follows  :  seeds  are  made  to  germinate  upon  some  clean 
support,  for  instance  moist  sponge  or 
cotton,  horse-hair  cloth,  or  perforated 
parchment-paper,  and  when  the  root 
of  the  seedling  is  a  few  centimeters 
long  and  the  plumule  is  somewhat 
developed,  the  plantlet  is  secured  to 
a  firm  support  at  the  surface  of  a  cy- 
lindrical glass  vessel,  in  such  a  man- 
ner as  to  allow  the  roots  to  dip  into 
the  nutrient  liquid  which  it  contains, 
while  the  body  of  the  seed  is  not  im- 
mersed. One  of  the  simplest  sup- 
ports for  the  plantlet  is  shown  in 
Fig.  145.  A  perforated  cork  is  cut 
in  halves,  and  the  two  parts  are  held 
together  by  a  spring.  The  pressure 
exerted  by  the  spring  is  sufficient  to 
keep  the  plantlet  in  place,  and  not 
enough  to  injure  it  in  any  way.  When  the  plant  has  attained 
the  height  of  a  few  inches,  it  is  well  to  provide  a  firm  rod  at  the 
side  of  the  cork,  so  that  the  stem  can  be  held  in  place.  Certain 
precautions  have  been  found  advantageous:  (1)  the  roots  in  the 
liquid  should  be  kept  darkened  ;  (2)  the  solution  should  be  fre- 
quently renewed. 

When  skilfully  managed,  this  method  of  culture  gives  very 


1  Woodward  (Philosophical  Transactions,  1699)  and  Duhamel  (Traite  des 
Arbres,  1765)  have  given  accounts  of  their  cultivation  of  various  plants  in 
this  way. 


250  WATER-CULTURE. 

satisfactory  results ;  in  man}-  cases  plants  have  been  carried 
safely  throughout  their  whole  development  from  seed  to  seed. 
The  principal  difficulties  arise  from  the  invasion  of  moulds,  and 
from  the  continual  changes  which  the  nutrient  solution  under- 
goes. 

670.  In  Tharandt,1  where  the  method  has  been  very  success- 
fully applied  in  numerous  series  of  cultures,  the  following  out- 
fit suffices:    (1)  small  glass  vessels  covered  with  gauze,  upon 
which  the  seeds  swollen  by  twelve  hours'  immersion  in  water, 
and   subsequent!}-  sprouted   on   filtering-paper,   are   placed  for 
further  development ;  (2)  wide-mouthed  vessels  of  the  capacit}', 
respectively,  of  one,  two,  and  three  liters,  each  of  which  is  pro- 
vided with  the  spring  and  cork  already  described. 

671.  By  the  careful  use  of  these  simple  appliances  the  role 
which  each  of  the  ash  constituents  plays  in  the  life  and  growth 
of  plants  has  been  ascertained.     But  although  there  is  a  sub- 
stantial agreement  among  experimenters  as  to  the  more  impor- 
tant points,  there  are  a  few  unsettled  questions.2 

672.  Normal  nutrient  solution.     It  is  plain  that  an   aqueous 
solution  of  the  salts  necessary  for  the  most  active  and  complete 
development  of  the  plant  should  have  these  salts  in  the  right 
proportion.     The  solution  advised  for  ordinary  use  in  the  above 
experiments  is  generally  known  as  the  Tharandt  normal-culture 
solution.     Nobbe  8  gives  the  proportions  as  follows  :  — 

1  Success  hi  water-culture  demands  the  closest  attention  to  all  the  external 
conditions  of  the  plant.    The  amount  of  light  and  heat  must  be  carefully  regu- 
lated, and  the  plants  must  be  kept  free  from  any  insects  and  parasitic  fungi. 
The  latter  is  one  of  the  most  difficult  and  discouraging  tasks  connected  with 
the  method  of  experimenting.     In  order  to  secure  the  best  surroundings  for 
the  cultivation  of  plants  in  water,  a  heavy  table  moving  with  wheels  on  rails 
has  been  employed  at  the  experiment-station  at  Tharandt ;  upon  this  the  glass 
vessels  can  be  carried  with  the  least  liability  to  jarring,  from  the  open  air  in 
the  daytime  to  a  suitable  protection  at  night  or  duiing  wet  weather. 

2  Moreover  it  is  to  be  borne  in  mind  that  the  conditions  of  water-culture 
are  very  unlike  those  of  ordinary  culture  in  respect  to  the  surroundings  of  the 
roots  themselves,  and  it  is  believed  that  to  this  difference  of  conditions  may  be 
ascribed  some  of  the  unsettled  questions.     The  root-hairs  developed  in  contact 
with  moist  particles  of  soil  are  not  the  same  as  those  grown  in  water  alone. 
To  avoid  this  possible  source  of  error,  various  finely  divided  substances  have 
been  suggested  as  a  proper  support  for  the  roots  and  rootlets  ;  for  instance, 
the  charcoal  from  sugar,  powdered  quartz,  etc.     When  these  are  employed,  the 
roots  of  the  plant  are  made  to  grow  directly  in  the  artificial  soil  which  is 
watered  with  the  experimental  solutions. 

3  By  the  use  of  this  solution  buckwheat  plants  can  be  carried  through  their 
entire  development,  as  is  shown  by  Nobbe,  in  Versuchs-Stationen,  1868,  p.  4. 
He  arranged  nine  plants  in  five  vessels,  each  of  three  litres  capacity,  in  such 


NUTRIENT   SOLUTIONS.  251 

4  Equivalents  of Potassic  chloride 

4  Equivalents  of Calcic  nitrate 

1  Equivalent  of     ...      Magnesic  sulphate  (crystallized) 

One  part  of  the  mixture  of  these  salts  is  to  be  dissolved  in 
one  thousand  parts  pure  water,  and  then  a  trace  of  ferric  phos- 
phate is  to  be  added,  and  at  times  during  any  culture  a  trace 
also  of  potassic  phosphate.  The  proportions  of  the  above  salts 
to  a  liter  of  water  are  given  as  follows  by  Bretfeld : l  — 

Gram. 

Potassic  chloride 207 

Calcic  nitrate 456 

Magaesic  sulphate 171 

673.  Pfefler  recommends  the  formula  suggested  by  Knop  :2  — 

Calcic  nitrate 4  parts  by  weight 

Potassic  nitrate 1  part  by  weight 

Magnesic  sulphate  (crystallized)   ...  1  part  by  weight 

Potassic  phosphate 1  part  by  weight 

These  salts  are  to  be  thoroughly  mixed  and  the  mixture  used 
in  the  proportions  of  y^Tf  ioW>  si<j  parts  of  water.  To  the 
solutions,  when  ready  for  use,  a  drop  or  two  of  a  solution  of 
some  iron  salt,  or  a  decigram  of  ferric  phosphate,  must  be 
added. 

674.  According  to  Knop,  the  first  of  the  solutions  mentioned 
above  (one  half  pro  mille)  is  as  dilute  as  can  be  useful :  and  on 
the  other  hand,  a  five  pro  mille  solution  is  as  strong  as  can  be 
employed  with  safety.     But  the  stronger  solution  should  be  used 
as  the  plant  comes  into  flower.     The  slight  turbiditv  which  is 
frequently  noticed  in  these  solutions  ma}*  be  disregarded. 

If  the  solutions  become  alkaline  while  in  contact  with  the 
roots,  as  they  are  very  apt  to  do,  a  trace  of  dilute  nitric  acid 
may  be  added  with  advantage.  But  it  must  not  be  forgotten 
that  it  is  best  in  every  case  to  renew  the  solutions  frequently, 
and  as  a  rule  to  emplo}'  them  in  tolerably  large  amounts. 
Moreover,  it  is  advantageous  to  pass  a  current  of  air  occasion- 
ally through  the  solutions  in  which  the  roots  are  placed,  for  the 
purpose  of  supplying  more  oxygen  to  them.8 

a  manner  that  1  and  2  contained  one  plant  each,  3  and  4  two  plants  each,  and 
5  three  plants. 

1  Das  Versuchswesen  auf  dem  Gebiete  der  Pflanzenphysiologie,  1884,  p.  120. 

2  Lehrbuch  der  Agricultur-Chemie,  i.  1868,  p.  605. 

8  For  solutions  for  the  cultivation  of  fungi  various  formulas  have  been  pro- 
posed, only  a  few  of  which  can  be  here  referred  to  :  (1)  3  to  8  grams  of  sugar 


252  WATER-CULTURE. 

675.  The  constituents  may  be  taken  up  by  the  roots  in  larger 
proportion  than  the  needs  of  the  plant  demand.     The  excess 
may  (1)  remain  in  solution  in  the  sap  of  the  plant,  (2)  may  es- 
cape to  a  slight  extent  through  superficial  parts,1  (3)  may  form 
insoluble  incrustations  or  concretions  upon  or  in  the  plant.2 

676.  The  office  of  the  different  ash  constituents.     Potassium. 
The  most  conclusive  evidence  in  regard  to  the  importance  of  this 
element  is  afforded  by  experiments  by  Nobbe,  Schroeder,  and 
Erdmann.8    Plants   of  Japanese   buckwheat  were   grown  in  a 
nutrient  solution  free  from  any  trace  of  a  potassium  salt.     Ex- 
amination after  a  few  weeks  showed  that  all  the  organs  of  the 
plants  were  free  from  starch,  and  that  although  the  points  of 
growth  remained  sound,  all  growth  had  practically  ceased.  Even 
in  the  chloroplryll-granules  not  more  than  a  trace  of  starch  could 
be  detected.     As  soon  as  a  salt  of  potassium  was  added  to  the 
water,  the  plants  began  to  grow  again,  and  thenceforth  the  de- 
velopment was  normal.     From  the  same  series  of  experiments  it 
appeared  that  the  chloride  was  the  best  form  in  which  potassium 
could  be  given  to  these  plants,  and  the  nitrate  the  next  best ;  while 
on  the  other  hand  the  phosphate  and  the  sulphate  appeared  to 
exert  a  less  favorable  effect    After  use  of  a  solution  of  the  latter 
salt  the  leaves  were  fleshy,  more  or  less  rolled  up,  and  it  was 
evident  that  the  starch  formed  in  them  was  not  transferred  to 
the   other   organs   of  the   plant.     Nobbe's   statement  follows : 
"  The  production  of  starch  in  the  leaves  is  not  dependent  upon 
the  form  in  which  potassium  is  afforded  to  the  plant,  but  this 

in  100  cubic  centimeters  of  water,  to  which  \  to  3  pro  mille  of  the  above  salts 
(see  673)  maybe  added,  and  also  a  trace  of  ammonic  tartrate  (Pfeffer,  Pflanzen- 
physiologie,  i.  p.  254)  ;  (2)  Pasteur  (Ann.  de  Chimie  et  de  Physique,  1862, 
p.  106)  recommends  the  addition  to  100  c.cm.  of  water,  of  10  grams  of  cane- 
sugar,  .5  gram  of  ammonic  tartrate,  and  .1  gram  of  the  ash  of  yeast ;  (3)  Nageli 
(Sitzungsb.  d.  bayer.  Akad.,  1879)  has  the  following  :  100  cm.  water,  3  grams 
cane-sugar,  1  gram  ammonic  tartrate,  4  grams  phosphoric  acid  neutralized  by 
the  ash  of  peas  or  wheat ;  (4)  Nageli  suggests  also,  for  the  cultivation  of 
Schizomycetes,  100  c.cm.  water,  .1035  gram  hydro-potassic  phosphate,  .016 
gram  magnesic  sulphate,  .013  gram  potassic  sulphate,  .0055  gram  calcic 
chloride. 

1  Sachs  (Botanische  Zeitung,  1862,  p.  264)  states  that  drops  of  water  placed 
on  the  leaves  of  Tropseolum  and  Cucurbita  are  found  after  a  time  to  be  alkaline. 
Saussure  (Recherches  chimiques,  1805,  p.  263)  asserts  that  if  leaves  of  fresh 
plants  are  washed  with  water,  the  ash  which  they  yield  on  combustion  is  found 
to  be  poorer  in  alkaline  salts  than  that  of  leaves  which  have  not  been  so  treated. 

2  Cystoliths  and  the  like,  the  incrustations  upon  certain  species  of  Saxi- 
frage, are  cited  as  examples  of  the  latter. 

»  Versuchs-Stationen,  xiii.,  1870,  p.  357. 


OFFICE   OF   THE   ASH   CONSTITUENTS.  253 

element  must  be  present  in  order  to  have  any  starch  formed. 
The  transport  of  the  starch  from  the  leaves  to  other  parts  is, 
however,  dependent  upon  the  form  in  which  the  potassium  is 
presented  to  the  plant,  and  for  this  purpose  the  chloride  is  most 
efficient." 

677.  Calcium  and  magnesium,.     These  elements  cannot  re- 
place one  another  in  the  plant,  though  it  is  not  clear  what  office 
they  perform.     Pfeffer  regards  it  as  possible  that  calcium  may 
play  an  important  part  in  the  formation  of  the  cell-wall,  inas- 
much as  it  can  always  be  detected  there.    Melnikoff  is  quoted  by 
Pfeffer  *  as  stating  that  in  the  cell-wall  calcium  generally  exists 
as  the  carbonate.     It  is  suggested  by  Sachs  that  this  element 
may  enter  into  combination  with  cellulose,  as  it  does  with  some 
other  carbohydrates. 

When  seedlings  ar.e  grown  in  pure  water  their  development 
after  a  short  time  becomes  completely  checked,  and  the  addition 
of  all  necessary  substances  except  calcium  salts  fails  to  stimulate 
a  normal  growth ;  but  after  the  addition  of  a  small  amount  of 
any  calcium  salt  the  normal  processes  of  the  plant  recommence 
at  once.2  Regarding  the  almost  universal  occurrence  of  calcic 
oxalate  in  plants,  Sachs  says:  "The  importance  of  calcium 
must  therefore  be  sought  partly  in  its  serving  as  a  vehicle  for 
sulphuric  and  phosphoric  acid  in  the  absorption  of  food-material, 
and  parth'  in  its  fixing  the  oxalic  acid,  which  is  poisonous  to 
the  plant,  and  rendering  it  harmless." 3 

678.  Phosphorus.     The  principal  and  perhaps  the  only  com- 
bination of  this  element  available  for  plants  is  phosphoric  acid 
(the  phosphates).    The  experiments  by  Ville  upon  the  absorption 
by  plants  of  calcic  phosphite  and  hypophosphite,  although  not 
conclusive,  make  it  appear  probable   that   these  salts  cannot 
replace  the  phosphate  in  absorption. 

It  is  not  clear  what  the  office  of  phosphorus  is  in  the  plant, 
but  in  some  of  its  compounds  it  is  so  often  associated  with  the 
soluble  albuminoids  that  it  is  believed  to  assist  in  the  transfer 
of  these  matters.  Schumacher  holds  that  the  chief  work  of  the 
alkaline  phosphates  is  the  acceleration  of  the  diffusion  of  these 
difficultly  diffusible  substances  (the  albuminoids).4  (See  957.) 

1  Pflanzenphysiologie,  i.,  1881,  p.  259. 

2  Boehm  :  Sitzungsb.  d.  Wien.  Akad.  Band  Ixxi.  Abth.  i.,  1875,  p.  481. 
8  Text-book,  2d  ed.,  1882,  p.  699. 

*  "  If  these  [alkaline  phosphates]  substances  are  mixed  with  a  solution  of 
albumin,  or  if  a  solution  of  them  is  permitted  to  diffuse  against  one  of  albumin, 
a  much  greater  amount  of  the  latter  will  pass  through  the  membrane  than 


254  WATEB-CULTUBE. 

679.  Iron.1    When  a  plant  is  provided  with  a  nutrient  solu- 
tion containing  all  essential  elements  except  iron,  its  chlorophyll- 
granules  fail  to  attain  complete  development.     They  remain  in 
an  imperfect  condition,  and  do  not  have  the  characteristic  green 
color.     Upon  the  addition  of  a  mere  trace  of  a  salt  of  iron  to  the 
solution  a  change  is  observable  at  once,  the  granules  assuming 
their  proper  shape  and  color.     Plants  grown  in  a  solution  with- 
out iron  have  a  pale  and  even  blanched  look,  which  at  once 
disappears  when  iron  is  added  ;  moreover,  a  local  effect  is  pro- 
duced when  a  solution  of  a  salt  of  iron  is  placed  on  the  surface 
of  the  blanched  leaves  of  such  plants,  —  a  green  color  is  given 
wherever  it  touches.     But  it  must  not  be  supposed  that  the  fail- 
ure of  some  leaves  to  produce  chlorophyll  at  certain  points  or 
spots  is  always  due  to  absence  of  iron. 

It  is  not  clear  that  iron,  which  is  .so  necessary  to  the  produc- 
tion of  chlorophyll,  enters  into  the  composition  of  either  the 
granule  or  the  pigment;  but  according  to  Pfeffer  there  is  a 
strong  probability  that  in  the  latter  it  exists  in  the  form  of  some 
organic  compound.  Iron  has  been  found  in  the  cell-walls  of  cer- 
tain algae2  (as  an  incrustation),  and  also  in  the  fruit  of  Trapa 
natans,  the  frond  of  Lemna  trisulca,  and  sparingly  in  other 
plants,  as  shown  by  the  analyses  collated  b}T  Wolff. 

680.  Chlorine.     This  element  appears,  from  experiments  by 
Nobbe 8  and  Beyer,4  to  be  indispensable  to  the  full  development 
of  some  plants  (e.  g.,  buckwheat),  but  it  is  not  required  for  many 
others  (e.  g.,  Indian  corn).8     Nobbe  concludes,  from  his  experi- 


would  otherwise  be  the  case.     In  the  life  of  the  plant  this  work  of  the  alkaline 
phosphates  plays  a  very  important  r61e  "  (Physik  der  Pflauze,  1867,  p.  129). 

1  That  iron  is  indispensable  to  the  full  vigor  of  plants  was  shown  by  Eusebe 
Gris  in  1843,  and  the  subject  was  further  studied  by  Arthur  Gris  in  1857. 
Salni-Horstmar  (in  1856),  Sachs,  and  others  have  added  much  to  the  knowledge 
of  the  subject,  showing  that  no  other  element  can  replace  iron  in  producing 
the  changes  noted  above. 

2  Cohn  :  Beitrage  zur  Biologie  der  Pflanzen,  1870,  p.  119. 

8  Versuchs-Stationen,  vii.,  1865,  p.  371  ;  xiii.,  1870,  p.  394. 

*  Versuchs-Stationen,  xi.,  1869,  p.  262. 

6  Knop :  quoted  by  Pfeffer,  Pflanzenphysiologie,  i.,  p.  259. 

The  conclusions  reached  by  Johnson  in  1868  appear  to  need  little  modifica- 
tion at  the  present  date.  "  1.  Chlorine  is  never  totally  absent.  2.  If  indis- 
pensable, but  a  minute  amount  is  requisite  in  the  case  of  the  cereals  and  clover. 
3.  Buckwheat,  vetches,  and  perhaps  peas,  require  a  not  inconsiderable  amount 
of  chlorine  for  full  development.  4.  The  foliage  and  succulent  parts  may 
include  a  considerable  quantity  of  chlorine  that  is  not  indispensable  to  the  life 
«f  the  plant"  (How  Crops  Grow,  p.  182). 


OFFICE   OP   THE    ASH    CONSTITUENTS.  255 

raents,  that  it  is  required  for  the  transfer  of  starch.  Associating 
this  view  with  what  is  known  regarding  the  office  of  potassium, 
it  is  easy  to  see  why  potassic  chloride  should  be  so  useful  a 
salt.1 

681.  Sulphur  is  absorbed  by  plants  in  the  form  of  the  soluble 
sulphates.     These  are  believed  to  undergo  immediate  decompo- 
sition in  the  plant ;  for  example,  calcic  sulphate  is  decomposed 
at  once  by  oxalic  acid,  and  calcic  oxalate  is  formed.     The  sul- 
phuric acid  thus  set  free  is  reduced,  the  sulphur  entering  into 
the  constitution  of  the  albuminoids2  (see  884). 

682.  Sodium  salts  cannot  wholly  replace  potassium  salts  in 
the  plant ;  nevertheless,  for  a  portion  of  the  potassium  needed 
by  the  plant  an  equivalent  amount  of  sodium  can  in  some  cases 
be  substituted.     It  has  been  found  possible  to  cultivate  success- 
fully* some  maritime  plants  which  normally  contain  a  certain 
amount  of  sodium  salts,  when  potassium  has  replaced  sodium 
in  the  water  furnished  to  the  plant. 

683.  Rarer  constituents.     Besides  the  ash  constituents  always 
detected  in  plants,  there  are  certain  elements  which  are  only 
occasionally  met  with  in  greater  or  less  amount,  and  these  will 
be  next  considered. 

684.  Silicium.      This  element  is  so  abundant  in  the  ash  of 
many  grasses,  Equisetacese,  etc.,  that  it  almost  claims  a  place 
in   the  list  of  indispensable  elements ;    but   experiments  have 
shown  abundantly  that  in  grasses  at  least,  the  proportion  of  it 
present  can  be  reduced  to  a  very  low  point  without  materiall}' 
affecting  the  vigor  of  the  plant  or  the  strength  of  the  culms. 
Thus  Sachs 8  showed,  in  1862,  that  the  amount  of  silicic  acid  in 
the  ash  of  Indian  corn  could  be  reduced  from  18  per  cent  to  .7 
per  cent,  without  injurious  effect  on  the  plant. 

685.  Zinc  has  been  detected  in  many  plants  grown  on  soil 
containing  it  in  considerable  amounts ;    for  instance,   that  at 
Altenberg4  (near  Aix).     Frej'tag5  found  that  all  plants  experi- 
mented upon  were  able  to  absorb  more  or  less  zinc  when  it 


1  Bretfeld  :  Das  Versuchswesen,  1884,  p.  134. 

2  Holzner  :  Flora,  1867.    An  interesting  paper  by  Hilgers  (Pringsh.  Jahrb., 
vi.,  1867,  p.  285)  gives  an  account  of  the  formation  of  crystals  of  calcic  oxalate 
in  various  parts  of  plants,  and  presents  certain  speculations  as  to  their  origin. 

3  Flora,  1862,  p.  53.     Further  experiments  are  recorded  by  Knop  (Ver- 
suchs-Stationen,  iv.,  1862,  p.  176),  Rautenberg  and  Kiihn  (Versuchs-Stationeu, 
vi.,  1864,  p.  359),  Birner  and  Lucanus  ( Versuchs-Stationen,  viil,  1866,  p.  141). 

*  Sachs  :  Handbuch  der  Experimental- physiologic,  1865,  p.  153. 
6  Chemisches  Central-blatt,  1870,  p.  517. 


256  WATER-CULTURE. 

was  offered  in  large  amount ;  nevertheless,  Gorup-Besanez J 
could  detect  none  in  peas  and  buckwheat  cultivated  in  a  soil 
containing  a  fair  amount  of  zinc  carbonate.  It  is  sometimes 
said  that  Viola  tricolor  and  Silene  inflata  grown  on  zinc  soil  take 
up  an  appreciable  amount  of  this  element ;  and  further,  that 
certain  plants  are  directly  affected  in  shape  by  the  presence  of 
zinc  in  the  soil ;  in  fact,  varieties  based  upon  this  supposed 
relation  have  been  described.  The  experiments  of  Hoffmann,2 
however,  throw  much  doubt  upon  the  relation  of  the  zinc  to  a 
change  of  form,  except  in  the  single  case  of  Viola  lutea. 

Aluminium 3  occurs  in  traces  in  many  plants,  while  in  species  of 
Lycopodiurn  (e.  g.  complanatum)  it  is  present  in  large  amount. 

Manganese 4  is  abundant  in  the  ash  of  Trapa  natans,  Quercus 
Robur,  and  Castauea  vesca. 

Caesium  and  Rubidium 5  have  been  detected  by  the  spectro- 
scope in  minute  amounts  in  many  plants. 

Fluorine6  has  been  found  in  the  ash  of  Lycopodium  clava- 
tum,  and  traces  of  it  in  other  plants.  Iodine  and  Bromine 7  are 
found  in  marine  algse,  in  much  smaller  proportions  in  aquatics 
growing  in  estuaries  (for  example,  Zostera),  and  in  minute 
amount  in  some  plants  grown  far  from  the  sea. 

Barium,  Strontium,  and  Silver  have  been  found  in  the  ash  of 
Fucus.  Mercury,  Lead,  Copper,  Cobalt,  Nickel,  Tin,  Thallium, 
Selenium,  Titanium,  and  Boron  have  all  been  found  by  analysts 
in  the  ash  of  certain  plants,  but  alwa}Ts  in  the  merest  traces. 
Arsenic8  has  also  been  detected  in  a  few  instances. 


1  Annalen  der  Chemie  und  Pharmacia,  cxxvii.,  1863,  p.  243.     This  paper 
contains  an  account  of  the  relations  of  agricultural  plants  to  metallic  poisons. 
Botanische  Zeitung,  1875,  p.  628. 

Knop:  Lehrbuch,  p.  263;  Kochleder:  Phytochemie,  1854,  p.  237. 
Wolffs  Die  Mittlere  Zusammensetzung  der  Asche. 

Laspeyres  :  Annalen  der  Chemie  uud  Pharmacie,  cxxxviii.,  1866,  p.  126. 
Salm-Horstmar  :  Annalen  der  Physik  und  Chemie,  cxi.,  1860,  p.  339. 
'  Chatin,  in  Comptes  Rendus,  Ixxxii.,  1876,  p.  128. 

8  Numerous  references  to  the  literature  of  this  subject  will  be  found  in 
Sachs's  Experimental-physiologic,  and  in  Mayer's  Lehrbuch  der  Agrikultur- 
chemie. 


CHAPTER  IX. 

TBANSFER   OF   WATER   THROUGH   THE   PLANT. 

686.  WATER  is  a  constituent  of  all  active  cells.     The  proto- 
plasmic body  of  the  celt  possesses  a  marked  affinity  for  it,  and 
up  to  a  given  point  can  abstract  it  from  the  ordinary  surround- 
ings, but  under  certain  conditions  releases  it  again.     If  a  water- 
plant  in  full  activity  is  removed  from  water  and  exposed  to  the 
air,  it  speedily  loses  by  evaporation  a  considerable  part  of  its 
constituent  water,  and  shows  the  effect  of  this  loss  by  a  col- 
lapsing of  its  cell- walls  and  by  a  withering  of  all  its  parts.      But 
if  only  a  small  portion  of  the  plant  is  lifted  above  the  surface 
of  the  water,  the  loss  which  takes  place  will  be  partially  sup- 
plied by  transfer  through  the  cells  remaining  submerged.     Two 
points  are  made  clear  by  this  simple  experiment :  (1)  evapora- 
tion goes  on  with  great  rapidity  from  the  exposed  surface  of  the 
plant ;  (2)  only  a  part  of  the  loss  of  water  can  be  made  good  by 
transference  from  submerged  portions. 

687.  Comparison  of  the  structure  of  a  water-plant  with  that 
of  an  ordinary  plant  adapted  to  growth  in  the  air  shows  that 
the  surface  of  the  latter  is  such  as  to  prevent  very  rapid  evapo- 
ration, and  also  that  the  loss  caused  by  the  evaporation  can  be 
made  good  if  the  lower  part  of  the  plant  remains  in  contact  with 
water.    In  other  words,  the  plant  (1)  has  a  surface  which  protects 
it  against  too  great  loss  of  water ;  and  (2)  is  provided  with  a 
system  by  which  the  needed  supply  of  water  can  be  replenished. 

688.  But  it  is  not  alone  by  evaporation  from  the  surface  that 
water  is  consumed  by  the  plant.     Wherever  growth  goes  on  or 
work  is  done,  water  is  consumed,  and  a  fresh  supply  is  required. 
The  question  of  the  transfer  of  water  is  therefore  a  general  one. 

SOME  OF  THE  RELATIONS  OF  WATER  TO  TISSUES. 

689.  The  cell-wall  which  separates  the  cavity  of  one  cell  from 
that  of  its  neighbor  is  a  permeable  membrane.     According  to 
the  hypothesis  of  Nageli  (see  588),  it  is  composed  of  solid  par- 
ticles (micellae),  each  of  which  is  enveloped  in  an  adherent  film 

17 


258       TRANSFER   OF   WATER   THROUGH   THE   PLANT. 

of  water,  and  thus  prevented  from  coming  in  contact  with  those 
around  it.  According  to  this  hypothesis,  all  the  water  in  a  cell- 
wall  is  practically  continuous,  and  can  flow  freely  between  the 
micellae ;  therefore,  if  a  cell  contains  its  maximum  amount  of 
water,  and  the  cell-wall  is  tense,  the  water  is  in  a  state  of  equi- 
librium. Likewise  in  a  tissue  containing  its  maximum  amount  of 
water  this  .is  in  equilibrium.  But  the  balance  can  be  easily  dis- 
turbed in  a  plant  by  evaporation  from  the  surface,  or  by  other 
causes  before  mentioned.  If,  however,  a  sufficient  part  of  the 
absorbing  surface  of  the  plant  is  in  contact  with  water,  the  bal- 
ance can  be  restored,  since  the  water  in  the  cell- walls  is  practi- 
cally continuous  with  that  in  the  surroundings.  The  equilibrium 
is  restored  by  the  transfer  of  the  water  outside  the  cell-wall  to 
the  cell-wall  itself,  and  thence  to  the  parts  within.  The  tendency 
to  the  restoration  of  the  equilibrium  of  water  in  a  plant  is  so 
great  that  root-hairs  can  abstract  even  the  firmh*  adherent  hygro- 
scopic water  from  particles  of  soil  (see  644).  From  the  roots  or 
other  absorbing  organs  the  water  passes  sooner  or  later  to  the 
place  of  consumption. 

690.  In  most  cellular  plants  and  in  masses  of  cellular  tissue 
all  the  cell-walls  have  substantially  the  same  capacity  for  transfer 
of  water ;  but  in  all  plants  which  possess  a  fibro-vascular  system 
the  transfer  takes  place  chiefly  by  means  of  the  lignified  cell- 
walls  ;  and  even  in  cellular  plants  like  mosses,  it  is  in  those  cells 
which  are  elongated  and  otherwise  differentiated  to  form  an  im- 
perfectly developed  framework  that  the  rapid  transfer  is  made. 

691.  Transfer  of  water  in  woody  plants.     In  ligneous  plants 
the  water  is  transferred  most  rapidly  through  the  woody  tissues. 
This  is  experimentally  proved  by  ' '  girdling  "  their  stems  ;  that 
is,  removing  a  ring  of  bark  without  injuring  the  wood.     For  a 
time  the  leaves  remain  fresh,  and  the  plants  appear  to  suffer 
only  slightly,  if  indeed  at  all.     An  early  experiment  in  regard 
to  the  transfer  of  water  is  that  by  Hales  (in  1731),  who  says  r1 
"'  I  cut  off  the  bark,   for  one  inch  length,  quite  round  a  like 
branch  of  the  same  oak ;   eighteen  days  after  the  leaves  were 
as  green  as  any  on  the  same  tree."     Further  experiments  have 
shown  that  the  rapid  transfer  is  made  chiefly  in  the  younger 
wood  of  the  stem,  and  not  in  the  heart-wood ;  and,  also,  that 
the  water  is  transferred  most  rapidly  in  the  portions  of  new  wood 
having  the  coarser  texture  known  as  spring  wood 2  (see  395). 

1  Statical  Essays,  i.,  1731,  p.  130. 

2  Sachs  :  Vorlesungen  iiber  Pflanzenphysiologie,  1882,  p.  275. 


PATH  AND  RATE  OF  TRANSFER.         259 

692.  The  converse  of  Hales's  experiment  is  equally  conclu- 
sive.    If  the  continuity  of  the  wood  of  a  stem  is  interrupted  by 
the  removal  of  a  short  truncheon  without  at  the  same  time  much 
injuring  the  bark,  the  leaves  wither  in  a  short  time.     Cotta * 
asserts  that   upon  a  shoot  of  willow  which  still  maintains  its 
connection  with  the  plant  through  the  bark,  but  has  had  a  sec- 
tion of  wood  removed,  the  leaves  will  wither  as  quickly  as  they 
would  upon  a  shoot  wholly  severed  from  the  parent  plant. 

693.  That  water  can  be  convej'ed  through  the  stem   in  a 
direction  opposite  to  its  normal  course  is  shown  in  an  experi- 
ment by  Hales  :    "I  took  a  large  branch  of  an  apple-tree,  and 
cemented  up  the  transverse  cut  at  the  great  end,  and  tied  a  wet 
bladder  over  it ;  I  then  cut  off  the  main  top  branch  where  it  was 
§  inch  diameter,  and  set  it  thus  inverted  into  a  bottle  of  water. 
In  three  days  and  two  nights  it  imbibed  and  perspired  four 
pounds  two  ounces  and  one  half  of  water,  and  the  leaves  con- 
tinued green  ;  the  leaves  of  a  bough  cut  off  the  same  tree  at  the 
same  time  with  this,  and  not  set  in  water,  had  been  withered 
forty  hours  before. "- 

694.  Determination  of  path  and  rate  of  transfer.    Two  modes 
of  experimenting  have  been  employed  in  order  to  ascertain  ex- 
actly the  patli  and  the  rate  by  which  water  is  transferred  through 
ligneous  plants.     The  first  of  these  consists  in  using  a  colored 
solution,  which,  when  taken  into  the  plant,  tinges  all  the  tissues 
with  which  it  comes  directly  in  contact.     The  stem  or  branch 
used  in  the  experiment  is  cut  sharply  off  and  its  end  is  plunged 
at  once  into  a  colored  solution,  for  instance,  of  some  aniline 
dye  or  some  colored  vegetable  juice.     As  the  liquid  ascends  the 
stem,  certain  portions  of  the  tissues  become  more  or  less  deeply 
tinged,  and  its  course  and  rate  of  ascent  can  be  traced  by  sec- 
tions made  at  any  given  time,  at  different  distances  above  the  cut 
end.    A  similar  method  has  been  also  emploj-ed  by  plunging  in 
colored  water  the  uninjured  roots  of  the  plant  to  be  examined.8 


1  Quoted  by  Pfeffer:  Pflanzenphysiologie,  i.  123. 

2  Statical  Essays,  i.,  1731,  p.  131. 

8  "  Quel  que  soit  le  liquide  employe  et  les  variations  de  1'experience,  les 
resultats  generaux  ont  peu  varie,  savoir  :  que  1'eau  coloree  ne  penetre  ni  par 
1'ecorce  ni  par  la  moelle,  mais  toujours  au  travers  du  corps  ligneux,  tant6t 
dans  toute  son  etendue,  quelquefois  dans  sa  partie  la  plus  jeune,  savoir,  1'ex- 
terieur  du  corps  ligneux  des  exogenes,  et  1'interieur  des  endogenes.  On  obtient 
ce  meme  resultat  general,  soit  qu'on  plonge  les  plantes  munies  de  toutes  leurs 
racines,  soit  qu'on  emploie  des  branches  coupees  "  (De  Candolle's  Physiologic 
vegetale,  p.  83). 


260       TRANSFER   OF    WATER   THROUGH   THE   PLANT. 

695.  The  two  objections  to  the  first  method  are  :  (1)  that  the 
protoplasmic  body  of  the  cell  resists  the  entrance  of  nearly  all 
coloring-matters,  therefore  with  many  dyes  it  is  necessary  to 
experiment  with  cut  stems  and  branches,  allowing  the  dye  to 
enter  at  the  cut  surface ;  but,  as  will  be  shown  later,  a  cut  sur- 
face which  has  been  exposed  to  the  air,  even  for  an  instant, 
loses  part  of  its  power  of  absorbing  water  ;  (2)  it  is  by  no  means 
certain  that  the  dye  passes  through  the  stem  as  rapidly  as  the 
water  in  which  it  is  dissolved.    That  it  does  not,  seems  more 
than  probable  from  the  simple  experiment  of  suspending  one 
end  of  a  strip  of  filter-paper  in  a  solution  of  any  dye ;  the  water 
will  rise  faster  than  the  dye,  and  form  a  moist  space  above  that 
part  of  the  paper  which  becomes  colored. 

696.  The   second  method  of  experimenting   is   based  upon 
the  ease  with  which  certain  chemical  substances  foreign  to  the 
plant  can  be  detected  in  it  if  once  they  can  be  introduced  into 
and  carried  through  its  tissues.     Dilute  solutions  of  salts  of 
lithium,  for  instance  the  citrate,  serve  best  for  this  method,  and 
Pfitzer  suggests  that  the}-  be  applied  to  the  roots  of  a  plant 
which  has  been  allowed  to  wilt  somewhat  from  drought. 

697.  The  two  objections  which  maybe  urged  against  the  second 
method,  are  :  (1)  the  chemical  used  may  cause  more  or  less  dis- 
turbance in  the  plant,  and  may  even  excite  disordered  processes, 
and  it  is  plain  that  no  correct  conclusions  relative  to  the  rapid- 
ity of  transfer  in  a  healthy  plant  can  be  drawn  from  one  which 
is  in  a  state  of  disease  ;  (2)  the  presence  of  a  diffusible  salt,  for 
instance  one  of  lithium,  may  change  the  osmotic  relations  of  the 
tissues  with  which  the  salt  comes  in  contact.     But  in  spite  of 
these  serious  difficulties,  these  methods  are  of  considerable  use 
when  cautiously  employed. 

698.  The  above  methods  indicate  that  the  most  rapid  transfer 
of  water  is  through  the  lignified  cell- walls  of  the  framework  of 
the  plant.     The  source  of  supply  at  the  root  furnishes  the  need- 
ful amount  of  water  to  the  ligneous  tissues  of  the  fibrils,  and 
these  convey  it  to  the  converging  bundles  which  constitute  the 
framework  of  the  plant.    In  the  leaves  the  framework  divides  and 
subdivides  to  form  the  network  of  the  leaf  blade,  and  here  the 
ligneous  cells  and  ducts  are  in  intimate  contact  with  the  paren- 
chyma cells  which  make  up  the  pulp  of  the  leaf.     That  water 
finds  its  way  by  preference  through  the  fibre-vascular  bundles 
even  in  the  more  delicate  parts,  is  shown  b}-  placing  the  cut 
peduncle  of  a  white  tulip,  or  other  large  white  flower,  in  a  harm- 
less dye,  and  then  again  cutting  off  its  end  in  order  to  bring  a 


KATE   OF   ASCENT   IN   THE   STEM.  261 

fresh  surface  in  contact  with  the  solution,  when  after  a  short 
time  the  dye  will  mount  through  the  flower-stalk  and  tinge  the 
parts  of  the  perianth  according  to  the  course  of  the  bundles. 

699.  Rate  of  ascent.     The  following  are  some  of  the  discor- 
dant results  obtained  by  the  methods  mentioned  in  694 :  — 

Name  of  plant.                    Bate  of  ascent  per  hour.  Observer. 

Prunus  Laurocerasus     .     .     42-100  cm McNab. 

Salix  fragilis 85    " Sachs. 

Vitis  vinifera 98   " " 

Nicotiana  Tabacum  ...          118    " " 

Helianthus 2200    " Pfitzer. 

700.  But  little  is  known  as  to  the  reason  of  the  high  conduct- 
ing power  of  ligneous  tissues.     That  it  is  not  wholly  due  to 
capillarity  (as  has  been  suggested  on  account  of  the  abundance 
of  ducts  of  small  calibre  in  most  wood) ,  is  shown  by  the  struc- 
ture of  the  wood  of  coniferous  plants  in  which  no  ducts  are 
present.     Again,  at  the  very  time  when  the  evaporation  from 
leaves  of  plants  is  most  rapid,  and  the  transfer  of  water  to  sup- 
ply the  loss  must  be  greatest,  the  cavities  of  the  ducts  are  not 
wholly  filled  with  liquid,  but  contain  a  considerable  amount  of 
air ;  whereas  according  to  the  theory  of  capillarity  they  should 
contain  only  liquid.     By  a  very  ingenious  series  of  experiments 
Sachs  has  determined  the  relative  amount  of  space  occupied  by 
the  cell-walls,  water,  and  cavities  in  several  fresh  woods.     In 
the  case  of  fresh  coniferous  wood  he  found  the  following  ratios 
in  100  cubic  centimeters  of  wood:  — 

Cell- wall,  reckoned  as  dry 24.81 

Water,  in  the  cell- wall  and  in  the  cavities 58.63 

Air-spaces 16.56 

But,  as  Sachs  says,  since  neither  intercellular  spaces  nor  ducts 
are  present  in  this  wood,  the  16.56  per  cent  of  air  must  be  con- 
tained in  the  cavities  of  the  wood-cells ;  and  further,  since  the 
cell-walls  can  take  up  only  about  half  their  volume  of  water 
(say  12.4  cubic  centimeters),  the  remainder  (46.23  c.c.)  must 
exist  in  the  cell-cavities. 

701.  The  method  of  determining  the  amount  of  water  held  by 
the  cell- walls  of  dry  wood  is  the  following :  — 

A  thin  cross-section  of  fresh  wood  is  hung  up  in  dry  air  until 
it  ceases  to  lose  weight.  During  drying  a  crack  appears,  run- 
ning from  the  centre  to  the  circumference.  After  ascertaining- 
the  weight  of  the  disc  thoroughly  dried  (at  100°  C.),  the  wood 
is  suspended  in  a  saturated  atmosphere  until  enough  water  is 


262      TRANSFER   OF   WATER    THROUGH   THE   PLANT. 

absorbed  to  cause  a  swelling  of  the  tissues  and  a  closing  of  the 
crack.  In  this  condition  it  is  safe  to  assume  that  the  cell-walls 
themselves  are  saturated,  but  that  there  is  no  liquid  water  in  the 
cavity  of  the  cells.  The  difference  between  the  weight  of  the  dry 
and  that  of  the  saturated  disc  gives  the  weight  of  the  water 
taken  up  and  held  ;  this,  converted  into  volume,  is  found  to  be 
approximately  one  half  that  of  the  space  occupied  by  the  cell- 
wall  itself. 

702.  The  water  which  is  taken  up  in  relatively  small  amount 
and  held  in  the  micellar  interstices  of  lignified  cell-wall  is  in  the 
state  of  equilibrium  previously  described.     When,  however,  this 
equilibrium  is  disturbed  by  evaporation  at  any  point,  there  is  an 
immediate  transfer  of  the  imbibed  water  to  that  point,  and  the 
loss  from  this  transfer  must  be  made  good  at  once  by  the  recep- 
tion of  more  water.     This  interstitial  transfer  ma}*  take  place 
through  any  length  of  woody  tissue,  provided  there  is  a  con- 
sumption of  the  water  at  one  extremity  and  an  adequate  supply 
at  the  other.     When  the  consumption  of  water  is  only  that  which 
is  due  to  the  opening  of  growing  buds,  or  to  some  chemical  pro- 
cess, a  slow  transfer  of  water  to  the  point  of  consumption 1  must 
take  place.     When,  however,  it  is  due  to  evaporation  from  the 
leaves,  the  transfer  is  exceedingly  rapid. 

703.  Boehm2  considers  the  ascent  of  water  in  ligneous  tissue 8 
to  be  "a  phenomenon  of  filtration  caused  by  differences  in  pres- 


1  A  similar  transfer  can  be  demonstrated  to  take  place  in  porous  inorganic 
matter,  for  instance  powdered  hydrated  gypsum.     If  a  long  tube  be  filled  with 
this  material  and  well  saturated  with  water,  one  end  being  placed  in  water 
and  the  other  exposed  to  a  dry  atmosphere,  the  continual  loss  by  evaporation 
above  will  be  made  good  by  water  brought  up  from  below. 

Jamin's  apparatus  for  demonstrating  the  pressure  exerted  by  the  imbibition 
of  water  by  a  porous  substance  consists  of  a  cylinder,  in  the  mouth  of  which 
can  be  placed  a  tightly  fitting  plug  of  wood,  through  which  passes  a  ma- 
nometer tube.  The  pulverulent  substance,  for  instance  zinc  oxide,  is  closely 
packed  in  the  interior  of  the  cylinder,  around  the  open  end  of  the  manometer, 
and  the  whole  apparatus  is  then  placed  in  water.  With  zinc  oxide  the  ma- 
nometer shows  a  pressure  of  five  atmospheres ;  with  powdered  starch,  more 
than  six  atmospheres.  If  a  manometer  is  similarly  placed  in  a  block  of  dry- 
chalk,  and  the  chalk  is  then  submerged,  a  pressure  of  three  to  four  atmos- 
pheres is  indicated  (Lemons  professees  devant  la  Societe  chimique,  Seance  du 
8  mars,  1861,  quoted  by  Deherain:  Cours  de  Chirnie  Agricole,  1873,  p.  165). 

2  Ann.  des  Sc.  nat,  ser.  6,  tome  vi.,  1878,  p.  236. 

8  As  might  be  expected,  woody  tissues  never  conduct  water  so  readily  in  a 
transverse  as  in  a  longitudinal  direction.  Experiments  with  regard  to  this  have 
been  conducted  by  Wiesner  (Sitzungsb.  d.  Wien  Akad.,  Bd.  Ixxii.  1  Abth., 
1875)  upon  cubes  of  wood,  Four  sides  of  these  were  protected  by  varnish 


RATE   OF   ASCENT   IN   THE   STEM.  263 

sure  in  contiguous  cells.  ...  In  parenchyrnatous  tissues  filled  with 
sap  the  movement  of  water  caused  by  evaporation  is  a  function 
of  the  elasticity  of  the  cell-walls  and  of  atmospheric  pressure." 

Herbert  Spencer  kas  shown  that  when  a  cut  stem  is  quickly 
bent  backwards  and  forwards  there  is  a  marked  increase  in  the 
rapidity  with  which  colored  fluids  ascend  through  it.  "  To 
ascertain  the  amount  of  this  propulsive  action,  I  took  from  the 
same  tree,  a  Laurel,  two  equal  shoots,  and,  placing  them  in  the 
same  dye,  subjected  them  to  conditions  that  were  alike  in  all 
respects  save  that  of  motion :  while  one  remained  at  rest,  the 
other  was  bent  backwards  and  forwards,  now  by  switching  and 
now  by  straining  with  the  fingers.  After  the  lapse  of  an  hour 
I  found  that  the  d}-e  had  ascended  the  oscillating  shoot  three 
times  as  far  as  it  had  ascended  the  stationary  shoot,  this  re- 
sult being  an  average  from  several  trials.  Similar  trials  brought 
out  similar  effects  in  other  structures."  * 

704.  Effect  upon  transfer  of  exposing  a  cut  surface  to  the  air. 
One  of  the  most  interesting  characteristics  of  the  woody  tissues 
in  relation  to  the  transfer  of  water  is  the  immediate  change 
which  the  cut  surface  of  a  stem  undergoes  upon  exposure  to  air, 
unfitting  it  for  its  full  conductive  work.  De  Vries 2  has  shown 
that  when  a  shoot  of  a  vigorous  plant,  for  instance  a  Helianthus, 
is  bent  down  under  water,  care  being  taken  not  to  break  it  even 
in  the  slightest  degree,  a  clean  sharp  cut  will  give  a  surface 
which  will  retain  the  power  of  absorbing  water  for  a  long  time  ; 
while  a  similar  shoot  cut  in  the  open  air,  even  if  the  end  is  in- 
stantry  plunged  under  water,  will  wither  much  sooner  than  the 
first.  Shoots  cut  in  the  manner  first  described  remain  turgescent 
for  several  days.  If  a  cut  shoot  placed  in  water  has  begun  to 

against  the  entrance  and  exit  of  water,  and  one  of  the  two  surfaces  remaining 
uncovered  was  placed  in  water,  the  other  exposed  to  air,  when  the  transfer  of 
water  through  the  wood  was  found  to  be  more  rapid  in  a  longitudinal  than  in 
a  transverse,  and  in  a  radial  than  in  a  tangential  direction. 

Another  method  of  experimenting  was  also  employed  by  him  :  five  sides  of 
a  cube  of  wood  were  surrounded  by  separated  portions  of  dry  calcic  chloride, 
and  the  remaining  side  was  placed  in  contact  with  water ;  the  difference  in 
rate  of  transfer  ascertained  by  comparing  the  weights  of  the  portions  of  calcic 
chloride  after  a  fixed  time  was  found  to  be  essentially  that  given  by  the  other 
method. 

Experiments  by  Sachs  (Arbeiten  des  botan.  Instituts  in  Wiirzburg,  1879, 
p.  298),  in  which  water  was  forced  in  different  directions  through  the  wood  of 
coniferous  stems,  showed,  however,  that  under  pressure  water  passes  through 
wood  more  readily  in  a  tangential  than  in  a  radial  direction. 

1  Transactions  of  Linnaean  Society,  xxv.,  1866,  p.  405. 

2  Arbeiten  des  botan.  Inst.  in  Wiirzburg,  L,  1874,  p.  292. 


264     TRANSFER  otf  WATER  THROUGH  THE 

wilt,  cutting  off  the  stem  a  little  higher  up  will  cause  it  to  regain 
in  part  the  power  of  absorption  which  it  lost  upon  exposure. 

705.  Although  osmosis  can  have  very  little  to  do  directly 
with  the  rapid  transfer  of  water  through  the  stem,  branches,  and 
leaves,  it  plays,  as  has  been  seen,  a  very  important  part  in  the 
introduction  of  water  into  the  plant,  and  in  supplying  the  requi- 
site amount  of  it  to  cells  which  lie,  so  to  speak,  away  from  the 
main  channel  of  transfer. 

706.  Pressure  and  "  bleeding."    If,  before  its  leaves  unfold, 
a  grape-vine  be  cut  off  near  the  root,  or  a  little  higher  up  on  the 
stem,  the  cut  surfaces  will  bleed  copiously.     The  part  connected 
with  the  roots  will  continue  to  yield  a  supply  of  watery  sap  for 
a  considerable  time.     The  flow  is  plainly  regulated  to  a  ver}- 
great  degree  by  the  surroundings  of  the  plant,  being  accelerated 
by  heat  and  checked  by  cold.     It  is  not  merely  passive ;  the 
application  of  a  suitable  pressure-gauge  shows  that  the  escaping 
liquid  exerts  much  force. 

One  of  the  early  experiments  on  this  subject  was  made  by 
Hales,1  who  found  the  pressure  in  the  case  of  the  grape-vine 
to  be  equal  to  thirty-eight  inches  (105  cm.)  of  mercury,  or  more 
than  forty-three  feet  of  water.  Other  experimenters  have 
reported  higher  figures;  for  example,  Clark2  found  in  Betula 
lenta  a  pressure  of  eighty-five  feet  of  water. 

707.  Pitra8  has  shown  that  a  certain  amount  of  pressure  is 
exerted  by  sap,  even  in  stems  which  have  been  severed  from 
the  parent  plant,  the  lower  extremity  being  placed  in  water. 
In  some  of  his  experiments  he  found  that  it  was  not  exerted 
at  once,  but  only  after  the  lapse  of  a  considerable  time.     He 
further  shows  that  a  considerable  pressure  is  exerted  by  the 
sap  which  flows  out  of  a  cut  stem  the  leaves  and  twigs  of  which 
are  submerged. 

708.  There  are  considerable  individual  differences  in  plants 
as  to  the  force  with  which  the  sap  flows  from  wounds.     Wilson 
found  that  while  one  specimen  of  Ampelopsis  quinquefolia  gave 


1  Statical  Essays,  i.,  1731,  p.  114. 

2  The  apparatus  for  demonstrating  the  pressure  can  be  easily  used.    Reduced 
to  its  simplest  terms,  it  consists  of  a  mercurial  pressure-gauge,  which  can  be 
securely  attached  to  the  wounded  part  of  the  plant.      To  the  stump  of  the 
plant  the  gauge  must  be  fastened  by  means  of  stout  rubber  tubing,  which  has 
been  made  to  fit  tightly  around  both  plant  and  tube,  and  then  wired  firmly 
to  prevent  the  escape  of  any  liquid.      Dahlia  variabilis,  Vitis  vinifera,  and 
Helianthus  annuus  are  good  plants  for  purposes  of  demonstration. 

8  Pringsheim's  Jahrb.,  xi.,  1878,  p.  437. 


PRESSURE  OF  THE  SAP.  265 

no  pressure  for  the  root-system,  another  showed  a  pressure  of 
twenty  centimeters  of  mercury. 

709.  Bleeding  is  not  by  an 3-  means  of  universal  occurrence  in 
wounded  plants.     Horvath  found  none  in  the  following  cases: 
Humulus  Lupulus,  Hedera  Helix,  Syringa  vulgaris,  and  Sam- 
bucus  nigra.     In  some  cases  there  appears  to  be  bleeding  only 
from  the  cut  root,  none  occurring  from  the  stem. 

710.  The  bleeding  from  a  plant  may  be  greatest  immediately 
after  the  wound  is  made,  or  it  may  in  a  few  cases  not  reach  a 
maximum  for  some  hours  or  even  days,  after  which  it  gradually 
declines  until  it  ceases.     It  may  recommence  after  the  wound 
is  reopened.     According  to  Hartig,1  bleeding  may  continue  in 
some  cases  for  a  month. 

711.  The  amount  of  sap  which  escapes  during  bleeding  is 
variable  even  in  the  same  species.     The  following  cases  show 
that  the  loss  is  very  large :  — 

Betula  papyracea,  24  hours,  63£  Ibs.  (Clark). 

Agave  Americana,  24  hours,  375  cubic  inches  (Humboldt). 

712.  Hofmeister  has  given  the  following  example,  to  show 
how  large  is  the  relative  amount  of  sap  which  can  flow  from  cer- 
tain plants.     From  a  specimen  of  Urtica  urens  (stinging  nettle), 
whose  root-system  had  a  volume  of  1,450  cubic  centimeters, 
there  escaped  in  2J  days  11,260  cubic  centimeters  of  sap. 

713.  The  pressure  at  the  cut  surface  of  a  plant  varies  widely 
in  any  given  case,  according  to  the  surroundings.    The  following 
details  of  an  experiment  by  Clark 2  will  indicate  the  variations 
in  pressure  noted  during  a  comparatively  short  time. 

"  A  gauge  was  attached  to  a  sugar-maple  March  31st,  three 
days  after  the  maximum  flow  of  sap  for  this  species.  .  .  .  The 
mercury  [in  the  gauge]  was  subject  to  constant  and  singular 
oscillations,  standing  usually  in  the  morning  below  [its]  zero, 
so  that  there  was  indicated  a  powerful  suction  into  the  tree, 
and  rising  rapidly  with  the  snn  until  the  force  indicated  was 
sufficient  to  sustain  a  column  of  water  many  feet  in  height. 
Thus  at  6  A.  M.,  April  21st,  there  was  a  suction  into  the  tree 
sufficient  to  raise  a  column  of  water  25.95  feet.  As  soon  as  the 
morning  sun  shone  upon  the  tree  the  mercury  suddenly  began 
to  rise,  so  that  at  8.15  A.  M.  the  pressure  outward  was  enough  to 

1  Botanische  Zeitung,  1862,  p.  89. 

2  JJeport  of  the  Secretary  of  the  Massachusetts  Board  of  Agriculture  for 
1873,  p.  187. 


266       TRANSFER    OF    WATER   THROUGH   THE   PLANT. 

sustain  a  column  of  water  18.47  feet  in  height,  a  change  repre- 
sented by  more  than  44  feet  of  water." 

714.  The  pressure  of  the  sap  rises  and  falls  with  the  tempera- 
ture.    The  greatest  pressure  in  ligneous  plants  is  found  when  a 
cold  night  is  followed  by  a  warm  morning.     This  has  been  ex- 
plained by  the  expansion  of  the  air  contained  in  the  wood-cells 
and  ducts.     Detrner  observed  the  greatest  outflow  of  sap  in  the 
case  of  the  herbaceous  plants  Begonia  and  Cucurbita  to  be  at  a 
temperature  of  from  25°  to  27°  C.,  and  that  the  outflow  ceased 
at  32°  for  Begonia,  at  43°  for  Cucurbita.1 

715.  Besides  the  variations  both  in  bleeding  and  in  pressure 
of  sap  due   to   external   influences    there  are  some  periodical 
changes  which  are  not  yet  satisfactoril}"  explained.     Baranetzky 
found  that  the  greatest  extravasation  of  sap  from  the  crown  of 
the  root  took  place  in  Riciuus  between  8  and  10  o'clock  A.  M.,  in 
Helianthus  annuus  between  12  M.  and  2  P.  M.,  and  in  Helianthus 
tuberosus  between  4  and  6  P.M.,  the  plants  being  under  essen- 
tially the  same  conditions. 

716.  The  great  pressure  exerted  by  sap  under  certain  condi- 
tions is  thus  explained  by  Sachs.     From  the  root-hairs,  into 
which  the  water  comes  by  osmosis,  it  passes  by  osmosis  into  the 
parenchymatous  cells  of  the  cortex.     "  But  a  difficulty  occurs  in 
answering  the  question  why  the  turgescent  cortical  cells  of  the 
root  expel  their  water  only  inwards  into  the  woody  tissues,  and 
not  also  through  their  outer  walls.     We  may,  however,  here 
be  helped  by  the  supposition  that  the  micellar  structure  of  the 
cell-walls  is  different  on  the  outer  and  inner  sides  of  the  cells, 
and  that  those  facing  the  exterior  of  the  root  are  best  adapted 
for  permitting  filtration  tinder  high  endosmotic  pressure."  2 

Among  the  recorded  experiments  which  show  a  great  root- 
pressure  is  one  by  Clark,  described  by  him  thus  :  "  A  gauge  was 
attached  to  the  root  of  a  black  birch-tree  as  follows.  The  tree 
stood  in  moist  ground  at  the  foot  of  a  south  slope  of  a  ravine, 
in  such  a  situation  that  the  earth  around  it  was  shaded  by  the 

1  A  full  and  satisfactory  treatment  of  this  subject  in  detail  will  be  found  in 
the  following  works  :  — 

Schroder  :  Beitrag  zur  Kenntniss  ilcr  Friihjahrsperiode  des  Ahorn  (Pringsh. 
Jahrb.,  vii.,  1869).  In  this,  the  spring  phenomena  of  the  maple  are  clearly 
given. 

Baranetzky  :  Untersuchungen  iiber  die  Periodicitat  des  Blutens  (Abhandl. 
des  naturforschende  Gesellschaft  zu  Halle,  1873).  In  this  memoir  the 
experiments  cover  a  wide  range. 

2  Text-book  of  Botany,  2d  English  edition,  1882,  p.  688. 


EXUDATION   OF   WATER   FROM   UNINJURED   PARTS.      267 

overhanging  bank  from  the  sun.  The  root  was  then  followed 
from  the  trunk  to  the  distance  of  ten  feet,  where  it  was  carefully 
cut  off  one  foot  below  the  surface,  and  a  piece  removed  from 
between  the  cut  and  the  tree.  The  end  of  the  root  was  en- 
tirely detached  from  the  tree  and  lying  in  an  horizontal  position 
at  the  depth  of  one  foot  in  the  cold,  damp  earth,  unreached  by 
the  sunshine,  and  for  the  most  part  unaffected  by  the  temper- 
ature of  the  atmosphere,  measured  about  one  inch  in  diameter. 
To  this  was  carefully  adjusted  a  mercurial  gauge  April  26th. 
The  pressure  at  once  became  evident,  and  rose  constantly  with 
very  slight  fluctuations,  until  at  noon  on  the  30th  of  April  it  had 
attained  the  unequalled  height  of  85.80  feet  of  water."1 

717.  Pfeffer2  attributes  the  tendency  of  water  to  pass  only 
inwards  into  the  wood}7  tissues  wholly  to  the  fact  that  upon  that 
side  of  the  cells  which  faces  the  interior  of  the  root  the  osmotic 
capacity  is  greater.     Within  the  plant  the  cell-walls  are  never 
saturated  with  pure  water ;  but  the  imbibed  liquid  is  different  on 
different  sides,  and  hence  the  plasma  membrane  in  contact  with 
the  sides  must  have  different  capacities  for  osmosis. 

718.  In  midwinter  or  in  earliest  spring  some  of  the  tissues 
of  ligneous  plants  are  stored  to  a  large  extent  with  starch  and 
other  solid  products  manufactured  during  the  previous  season. 
At  the  coming  of  warmer  weather  chemical  changes  take  place, 
largely  following  the  absorption  of  water,  by  which  these  solid 
substances  are  transformed  into  a  liquid  state,  occupy  a  greater 
space  than  before,  and  of  course  exert  much  greater  pressure. 
The  saccharine  sap  of  the  maple  represents   that  which  dur- 
ing the  early  winter  existed  in  the  tissues  as  starch}-  matter. 
This   conversion  of  material  will   be  further  discussed   under 
' '  Metastasis." 

719.  Exudation  of  water  from  uninjured  parts  of  plants.     Un- 
der certain  circumstances  water  can  exude  in  a  liquid  form  from 
uninjured  parts  ;  for  instance,  through  chinks  or  rifts  in  the  leaf- 
tips  of  many  monocotyledonous  plants,  and  through  water-pores 
of  dicotyledons,  especially  when   these   are  young.      Musset 8 
reports  eighty-five  drops  of  liquid  falling  in  one  minute  from 
the  tip  of  a  leaf  of  Colocasia  esculenta.     Duchartre4  gives  the 
following  figures :    Twenty-five  drops  fell  in  one  minute  from 

1  Report  of  the  Secretary  of  the  Mass.  Board  of  Agriculture  for  1873,  p.  189. 

2  Pflanzenphysiologie,  i.,  1881,  p.  170. 
8  Comptes  Rendus,  Ixi.,  1865,  p.  683. 

*  Ann.  des  Sc.  nat.  hot,  ser.  4,  tome  xii.,  pp.  247,  250. 


268       TRANSFER   OF   WATER   THROUGH  THE   PLANT. 

the  tip  of  a  leaf  of  Colocasia  antiquorum,  and  22.6  grams  of 
liquid  were  collected  in  one  night.  From  the  young  leaves  of 
certain  Aroids  water  is  sometimes  ejected  in  a  fine  jet  to  a 
distance  of  a  few  inches.1  In  these  and  the  previous  cases  the 
liquid  escapes  through  rifts. 

TRANSPIRATION. 

720.  The  evaporation  of  water  from  the  surface  of  the  younger 
parts  of  plants  exposed  to  the  air  makes,  as  has  now  been  seen, 
a  continual  draught  upon  the  sources  of  water-supply.      But 
while  evaporation  from  the  free  surface  of  water  or  from  any 
dead  membrane  ceases  in  an  atmosphere  saturated  with  moisture, 
there  is  some  experimental  evidence  to  show  that,  under  certain 
conditions  of  radiation,  evaporation  from  the  living  plant  may 
continue  to  take  place  even  when  the  atmosphere  is  completely 
saturated.     This  difference  between  evaporation  from  a  free  sur- 
face and  that  from  a  plant,  although  not  fully  established,  ren- 
ders it  advisable  to  employ  for  the  latter  phenomenon  the  term 
transpiration.     This  term  is  sometimes   employed   in   Physics 
with  another  signification ;  but  its  prior  use  in  Vegetable  Physi- 
ology should  prevent  any  confusion. 

721.  Stomata.     Neither  through   the  cutinized   cell-walls   of 
the   epidermis,  nor  through   the   suberized   cell-walls   of  cork, 
can   transpiration  take    place  to  any  extent;  2  but  at  myriads 
of  points  in  the  epidermis  of  leaves  and  young  stems  there  are 
minute  orifices  which  permit  the  air  outside  the  plant  to  come 
into  communication  with  the  air  within.     It  has  been  shown  in 
Part  I.  that  these  openings,  the  stomata,  possess  definite  rela- 
tions as  regards  position  to  the  intercellular  spaces  below  them, 

1  Musset :  Comptes  Rendus,  1865. 

Muntingh(1672),  according  to  a  reference  in  Flora  (1837,  p.  717),  noted  the 
projection  of  a  small  jet  of  water  from  the  leaf  of  an  Aroid,  as  from  a  fountain. 

2  "It  is  of  the  highest  significance  that  those  plants  which  are  submerged, 
or  those  parts  of  plants  which  grow  in  the  ground  and  therefore  cannot  lose 
water  by  transpiration,  possess  a  cuticle  which  permits  water  and  dissolved 
matters  to  pass  through  with  comparative  facility  ;  while  the  parts  growing 
in  the  air  have  a  cuticle  of  a  different  quality,  through  which  water  passes  only 
with  difficulty,  and  thus  they  are  protected  from  too  great  a  loss  of  water  " 
(Pfeffer :  PHanzenphysiologie,  i.,  1881,  p.  139). 

The  amount  of  aqueous  vapor  which  can  escape  through  cuticle  is  very 
small.  According  to  Boussingault,  .005  gram  of  water  may  evaporate  in  one 
hour  from  one  square  centimeter  of  the  rind  of  an  apple,  while  from  the  surface 
of  a  peeled  apple  fifty-five  times  as  much  is  lost  ( Agronomic,  vi.,  1878,  p.  349). 


MECHANISM  OF   STOMATA.  269 

so  that  they  may  be  fairly  regarded  as  a  part  of  the  system  for 
aerating  the  plant. 

722.  By  reference  to  the  structure  of  the  more  common  kinds 
of  leaves  (see  Chapter  III.),  it  will  be  seen  that  the  terminations 
of  the  delicate  fibrils  of  the  framework  approach  very  closely 
to  the  aeriferous  spaces,  and  thus  by  the  uninterrupted  com- 
munication between  the  minute  fibrils  in  the  root-system,  the 
stem- system,  and  the  leaf-system  of  the  plant,  water  which  has 
been  absorbed  by  the  roots  is  brought  finally  to  the  parenchyma 
cells   which   surround   the   spaces   under   the    stomata.      If  it 
evaporates  from  the  outer  side  of  the  wall  of  these  cells  into 
the  intercellular  spaces,  the  water  may  make  its  escape  through 
the  stomata. 

723.  Stomata  are  not  mere  epidermal  rifts  having  an  aper- 
ture of  unvarying  width.     The  guardian  cells  of  a  stoma  are  so 
arranged  with  respect  to  each  other  and  the  proper  epidermal 
cells  contiguous  to  them,  that  the  width  of  the  opening  between 
them  can  be  increased  or  diminished  upon  certain  changes  in 
the  surrounding  conditions. 

724.  Mechanism  of  Stomata.     In  examining  the  mechanism  of 
stomata  it  is  necessary  to  distinguish  between  their  three  parts 
which  are  shown  in  a  vertical  section ;  namely,  (1)  the  anterior 
groove,  (2)  the  cleft,   and  (3)  the   posterior  groove,  which  is 
usually  continuous  with  an  intercellular  space.     It  is  plain  that  a 
stoma  is  most  widely  open  when  the  edges  of  the  cleft  are  farthest 
apart  and  the  rim  of  the  cup  not  closed.     Hence  an  inspection 
of  the  anterior  face  of  a- stoma  is  not  sufficient  to  show  whether 
the  stoma  is  most  widely  open  ;  the  width  of  the  cleft  itself  must 
be  ascertained. 

725.  In  distinction  from  proper  epidermal  cells,  the  guardian 
cells  contain  chlorophyll,  and  hence  under  the  influence  of  light 
can  produce  carbohydrates  (see  "Assimilation").     As  might  be 
expected,  the  osmotic  tension  is  different  in  these  two  groups 
of  cells. 

726.  The   following   account,    condensed   from   Strasburger, 
shows  the  relations  which  the  guardian  cells  sustain  to  those 
around  the  stoma  as  regards  the  thickness  of  the  walls.     The 
guardian  cells  are  strongh*  thickened  on  the  upper  and  under 
angles  of  the  walls  of  their  opposed  faces,  while  elsewhere  their 
walls   are  relatively  thin.      At  the   cleft    there    are    opposing 
projections  forming  its  edges.      The  opening  and  closing  of  a 
stoma  depend  upon  the  difference  in  the  thickness  of  the  parts 
of  the  walls.     When   the   turgescence  of  the  guardian  cells 


270     TRANSFER  OF  WATER  THROUGH  THE  PLANT. 

increases,  they  curve  more  strongly,  and  the  cleft  widens ;  but 
when  their  turgescence  diminishes,  the  cleft  becomes  straighter 
and  narrower,  it  being  clear  that  with  increasing  turgescence 
the  guardian  cells  must  become  more  convex  on  the  side  of 
least  resistance,  and  more  concave  upon  the  side  of  greatest 
resistance. 

727.  Relations  of  stoinata  to  external  influences.     In  a  classical 
series  of  experiments  upon  the  relations  of  stomata  to  their  sur- 
roundings, Mohl  *  has  shown  that  when  the  uninjured  leaves  of 
certain  orchids,  lilies,  etc.,  are  wet  with  water,  the  clefts  of  the 
stomata  open ;  but  these  plants  form  exceptions  to  the  general 
rule,  for  it  was  found  that  in  the  greater  number  of  cases  studied 
the  cleft  closes  when  the  stoma  is  brought  in  contact  with  water. 
In  Amaryllis  and  the  grasses,  this  closing  takes  place  with  great 
rapidity. 

728.  When  a  thin  film  of  epidermis  with  its  stomata  is  de- 
tached, and  examined  under  the  microscope,  the  behavior  is  the 
reverse  of  that  above.     In  a  detached  film  the  guardian  cells  of 
the  stoma  are  partially  freed  from  the  action  of  the  contiguous 
proper  epidermal  cells,  and  as  a  result  the  cleft  widens  when 
water  is  applied,  the  turgescence  being  increased  ;  but  if  a  solu- 
tion of  sugar  in  water  is  employed,  the  cleft  grows  narrower, 
since  the  turgescence   of  the  cells   is  at  once   diminished   by 
osmosis. 

According  to  Mohl,  in  a  wilted  leaf  the  clefts  of  the  stomata 
are  partially  or  wholl}'  closed,  but  the  application  of  water  causes 
them  to  open.  If  kept  wet,  they  soon  close  again. 

729.  The  cleft  of  a  stoma  opens  more  widely  in  the  light 
than  in  darkness ;  thus  leaves  of  Lilium  which  have  been  kept 
in  the  dark  in  a  saturated  atmosphere  for  some  days  have  the 
stomata  closed,  and  when  wet    the   cleft  opens  only  slightly. 
Upon  exposure  to  sunlight,  the  cleft  gradually  opens. 

730.  According  to  Van  Tieghem,2  stomata  are  always  open 
in  sunlight  and  closed  in  darkness.      In  order  to  cause  open 
stomata  to  close,  it  is  merely  necessar}-  to  suddenly  change  the 
amount  of  light.    This  closing  of  the  stomata  takes  place  in  half 
an  hour  when  a  bright  light  is  replaced  by  diffused  light. 

It  has  been  found  that  heat  has  no  marked  effect  upon  the 
opening  and  closing  of  stomata ;  thus  when  a  plant  is  kept  in 
darkness  at  a  temperature  of  from  15°  to  17°  C.,  they  are  closed, 

1  Botanische  Zeitung,  1856. 

2  Traite  de  Botanique,  1884,  p.  636. 


AMOUNT   OF   TRANSPIRATION. 


271 


and  will  not  open  when  the  plant,  still  kept  in  darkness,  is 
subjected  to  a  higher  temperature,  say  from  27°  to  30°  C. 

731.  From  the  foregoing,   it  appears  (1)  that  stomata  are 
delicately  balanced  valves,  which  are  exceedingly  sensitive  to 
external  influences;  (2)  that  in  wilted  leaves  they  are  partially 
closed ;    (3)  that  in   most   cases,  on  the  application  of  liquid 
water,  stomata  which  are  open  close  ;  (4)  that  strong  light  causes 
stomata  to  open  widely  ;  (5)  that  a  sudden  shock  causes  them  to 
close. 

732.  Amount  of  water  given  off  in  transpiration.1     This  is 
determined  chiefly  by  the  balance. 

In  the  oft-cited  experiment  of  Hales,2  in  1724,  the  amount 


1  The  earliest  experiments  upon  this  subject  appear  to  have  been  those  by 
Woodward  in  1699  (Philosophical  Transactions).  They  were  made  from  July 
to  October,  and  gave  the  following  results  (here  reduced  for  convenience  to 
grams)  :  — 


Name  of  plant  and  kind  of 
water  furnished. 

First  weight  of 
the  plant. 

Final  weight  of 
the  plant. 

Total  amount  of 
water  evaporated. 

Mint  in  rain  water    .    .    . 
Mint  in  spring  water     .    . 
Mint  in  Thames  water  .    . 
Pea  in  spring  water  .    .    . 

1.79 
1.72 
1.79 

6.27 

2.88 
2.68 
3.45 
6.46 

192.3 
163.6 
159.5 
160. 

Woodward's  most  interesting  observations  relate  to  the  ratio  of  growth  to 
evaporation  when  plants  are  cultivated  in  different  kinds  of  water.  Thus 
when  mint  was  grown  in  water  mixed  with  garden  earth,  the  ratio  of  growth 
to  evaporation  was  1 : 52  ;  but  when  it  was  grown  in  distilled  water,  1 : 214. 

2  "July  3,  1724,  in  order  to  find  out  the  quantity  imbibed  and  perspired 
by  the  Sun-Flower,  I  took  a  garden-pot  with  a  large  Sun-Flower,  3  feet  -+-  £ 
high,  which  was  purposely  planted  in  it  when  young ;  it  was  of  the  large 
annual  kind. 

"  I  covered  the  pot  with  a  plate  of  thin  milled  lead,  and  cemented  all  the 
joints  fast,  so  as  no  vapour  could  pass,  but  only  air,  thro'  a  small  glass  tube 
nine  inches  long,  which  was  fixed  purposely  near  the  stem  of  the  plant,  to 
make  a  free  communication  with  the  outward  air,  and  that  under  the  leaden 
plate. 

"I  cemented  also  another  short  glass  tube  into  the  plate,  two  inches  long 
and  one  inch  in  diameter.  Thro'  this  tube  I  watered  the  plant,  and  then 
stopped  it  up  with  a  cork  ;  I  stopped  up  also  the  holes  at  the  bottom  of  the 
pot  with  corks. 

"  I  weighed  this  pot  and  plant  morning  and  evening,  for  fifteen  several  days, 
from  July  3,  to  Aug.  8,  after  which  I  cut  off  the  plant  close  to  the  leaden 
plate,  and  then  covered  the  stump  well  with  cement ;  and  upon  weighing 
found  there  perspired  thro'  the  unglazed  porous  pot  two  ounces  every  twelve 


272       TRANSFER   OF    WATER   THROUGH   THE   PLANT. 

transpired  from  a  vigorous  sunflower,  three  feet  and  a  half  high, 
during  twelve  hours  of  a  very  warm  day,  was  one  pound  four- 
teen ounces,  and,  on  an  average,  one  pound  four  ounces  was 
transpired  every  twelve  hours.  Any  evaporation  from  the  sur- 
face of  the  soil  in  the  flower-pot  in  which  the  plant  was  growing 
was  prevented  by  a  lead  cover. 

A  still  simpler  method  of  preventing  evaporation  is  to  en- 
velop the  flower-pot  with  a  thin  rubber  membrane,  and  tie  this 
tightly  around  the  stem  of  the  plant.  A  fresh  supply  of  water 
can  be  given  to  the  plant  at  any  time  by  means  of  a  tube  close 
to  the  stem.  In  experiments  upon  transpiration  the  plant  should 
be  weighed  frequently,  care  being  taken  to  note  all  the  external 
conditions,  such  as  light,  moisture  of  the  atmosphere,  etc.  For 
weighing,  an  open  balance  with  large  pans  should  be  used.  The 
form  known  as  the  box  scale  will  answer  all  ordinary  purposes ; 
but  for  delicate  weighings  one  of  special  construction,  having  a 
long  beam,  is  preferable. 


hours  day,  which  being  allowed  in  the  daily  weighing  of  the  plant  and  pot,  I 
found  the  greatest  perspiration  of  twelve  hours  iu  a  very  warm  dry  day,  to  be 
one  pound  fourteen  ounces ;  the  middle  rate  of  perspiration  one  pound  four 
ounces.  The  perspiration  of  a  dry  warm  night,  without  any  sensible  dew,  was 
about  three  ounces  ;  but  when  any  sensible,  tho'  small  dew,  then  the  per- 
spiration was  nothing  ;  and  when  a  large  dew,  or  some  little  rain  in  the  night, 
the  plant  and  pot  was  increased  in  weight  two  or  three  ounces.  N.  B.  The 
weights  I  made  use  of  were  Avoirdupoise  weights. 

"I  cut  off  all  the  leaves  of  this  plant,  and  laid  them  in  five  several  parcels, 
according  to  their  several  sizes,  and  then  measured  the  surface  of  a  leaf  of  each 
parcel,  by  laying  over  it  a  large  lattice  made  with  threads,  in  which  the  little 
squares  were  ^  of  an  inch  each  ;  by  numbering  of  which  1  had  the  surface  of 
the  leaves  in  square  inches,  which  multiplied  by  the  number  of  the  leaves  in 
the  corresponding  parcels,  gave  me  the  area  of  all  the  leaves  ;  by  which  means 
I  found  the  surface  of  the  whole  plant,  above  ground,  to  be  equal  to  5616 
square  inches,  or  39  square  feet. 

"  I  dug  up  another  Sun-Flower,  nearly  of  the  same  size,  which  had  eight 
main  roots,  reaching  fifteen  inches  deep  and  sideways  from  the  stem  :  It  had 
besides  a  very  thick  bush  of  lateral  roots,  from  the  eight  main  roots,  which  ex- 
tended every  way  in  a  Hemisphere,  about  nine  inches  from  the  stem  and  main 
roots. 

"  In  order  to  get  an  estimate  of  the  length  of  all  the  roots,  1  took  one  of  the 
main  roots,  with  its  laterals,  and  measured  and  weighed  them,  and  then 
weighed  the  other  seven  roots,  with  their  laterals,  by  which  means  I  found  the 
sum  of  the  length  of  all  the  roots  to  be  no  less  than  1448  feet. 

"And  supposing  the  periphery  of  these  roots  at  a  medium,  to  be  }%  of  an 
inch,  then  their  surface  will  be  2286  square  inches,  or  15.8  square  feet ;  that 
is,  equal  to  §  of  the  surface  of  the  plant  above  ground  "  (Vegetable  Staticks, 
2d  ed.,  1731,  vol.  i.  p.  4). 


KBUTJZKf  4J   APPARATUS. 


273 


733.  Vesque  has  devised  an  automatic  apparatus1  by  which 
the  disturbance  of  the  equilibrium  of  the  balance  as  the  water 
evaporates  can  be  recorded  upon  a  revolving  drum.      In  this 
apparatus,  as  soon  as  the  needle  records  the  moment  of  descent 
of  the  beam,  an  electrical  current  releases  a  valve  so  as  to  per- 
mit the  passage  of  a  sufficient  quantity  of  mercury  to  the  losing 
side  of  the  balance  to  restore  the  equilibrium. 

734.  The  registering  apparatus  of  Krutizky2  is  simple,  but 
unfortunately  can  be  used  only  with 

cut  stems  or  branches.  It  consists 
of  a  U-tube  filled  with  water,  in  one 
end  of  which  a  leaf  or  stem  (cut  off 
under  water)  is  inserted,  through  a 
tightly  fitting  cork.  Through  a  cork 
in  the  other  end  extends  the  short 
leg  of  a  siphon.  In  a  jar  of  water 
there  floats  a  tube  balanced  to  keep 
it  erect.  This  is  somewhat  like  an 
hydrometer  (but  open  at  the  top), 
and  contains  a  certain  amount  of 
water  into  which  comes  the  long  leg 
of  the  siphon.  When  by  evapora- 
tion from  the  plant  water  is  drawn 
up  through  the  siphon  out  of  the 
floating  tube,  the  tube  (called  a 
"•swimmer")  of  course  becomes 
lighter  and  rises  in  the  jar.  If  an 

index  is  attached  to  the  swimmer,  as  in  the  figure,  it  can  be  used 
to  record  upon  a  revolving  drum  the  rise  of  the  swimmer  as  the 
plant  transpires.  To  prevent  evaporation  from  the  water  in  the 
jar  and  in  the  swimmer,  its  surface  is  covered  by  a  film  of  oil.8 

735.  When  a  transpiring  plant  is  placed  under  a  bell-jar,  a 
certain  amount  of  the  transpired  water  will  collect  upon  the 
inside  of  the  jar,  —  often  a  sufficient  quantity  to  appear  as  large 


1  For  a  full  account  of  its  construction  see  Annales  des  Sc.  nat.,  ser.  6, 
tome  vi.,  1878,  p.  186. 

2  Botanische  Zeitung,  1878,  p.  161. 

3  A  simpler  piece  of  apparatus  arranged  by  Pfeffer  answers  well  for  class 
demonstration.     It  is  easily  understood  from  Fig.  147.     The  fall  of  water  in 
the  small  lateral  tube  is  very  marked,  but  attention  should  be  called  to  the 
varying  pressure  caused  by  the  constantly  changing  level  of  the  water  in  the 
tube. 

FIG.  146.    Krutizky's  apparatus. 
13 


274      TRANSFER    OF    WATER    THROUGH    THE   PLANT. 


drops.  This  method  of  demonstrating  transpiration  has  been 
used,  when  somewhat  modified,  by  many  investigators,  notably 
Deherain.1  It  is  well  adapted  to  class  experiments,  since  very 
simple  appliances2  can  be  used :  for  instance, 
a  leafy  stem  can  be  inserted  in  a  piece  of 
pasteboard,  and  the  cut  end  of  the  stem 
placed  in  a  tumbler  of  water ;  another  tum- 
bler, inverted  over  the  stem,  rests  on  the 
pasteboard.  The  water  in  the  lower  tumbler 
is  prevented  from  evaporating  into  the  upper 
one.  The  amount  of  water  which  collects  on 
the  inside  of  the  upper  tumbler  comes  wholly 
from  the  transpiration  of  the  plant,  and  will  be 
found  to  vary  according  to  the  surroundings 
(see  page  275  et  seq). 

736.      If  a    weighed 
amount  of  calcic  chlo- 
ride   is    placed   with  a 
transpiring    plant   in    a 
confined  atmosphere,  the 
salt  will  readily  take  up 
the  aqueous  vapor,  and 
its  increase  in 
weight  gives 
the  amount  of 

water  exhaled  \>y  the  plant.  This 
method  of  measuring  the  amount 
of  transpiration  has  been  em- 
ployed by  several  experimenters, 
who  have  obtained  results  sub- 
stantially in  accord.  It  must  be 
noted,  however,  that  in  this 
method  the  air  to  which  the 
plant  is  exposed  is  rendered  ab- 
normally dry  by  the  presence  of 
the  salt,  and  the  plant  is  there- 
fore subjected  to  an  unusual  draft  upon  its  water-supply. 

737.   Garreau's  method  of  comparing  the  relative  amounts  of 
transpiration  on  opposite  sides  of  a  leaf  is  based  on  that  last 

1  Cours  cle  Chiinie  Agricole,  1873,  p.  180  et  seq. 
'2  Henslow.     See  Oliver's  Botany  (1864),  p.  15. 

PIG.  147.    Apparatus  for  demonstration  of  transpiration. 
Fio.  148.    Garreau's  apparatus. 


TRANSPIRATION    AND    EVAPORATION    COMPARED.      275 

mentioned,  and  is  of  easy  application.  Two  tubulated  bell-jars, 
each  furnished  with  a  mercury  trap  (m  and  m'),  are  secured  firmly 
with  soft  wax  to  opposite  sides  of  any  large  leaf.  In  each  bell- 
jar  is  a  small  capsule  (c  and  c')  containing  dry  calcic  chloride  of 
known  weight.  After  a  given  time  the  salt  placed  in  each  bell- 
jar  is  weighed,  and  the  excess  over  its  original  weight  shows  the 
amount  of  water  transpired.  The  following  are  some  of  Gar- 
reau's  results :  — 

(1)  The  quantity  of  water  exhaled  by  the  upper  face  of  a 
leaf  is  to  that  exhaled  by  the  lower  as    1:1,    1:3,  or  some- 
times as  1  :  5. 

(2)  There   are  marked  but  not  exact  relations  between  the 
quantity  of  water  exhaled  and  the  number  of  stomata.1 

738.  Transpiration   compared  with   evaporation   proper.     The 
evaporation  from  a  given  surface  of  water  is  between  three  and 
six  times  as  great  as  that  from  an  equal  surface  of  green  leaves 
similarly  exposed.     Unger2  found  that  leaves  of  Digitalis  pur- 
purea  with  a  surface  of  five  thousand  square  millimeters  tran- 
spired from  3.232  to  1.232  grams  in  a  given  time  ;  while  from  an 
equal  surface  of  water  from  4.532  to  8.459  grams  evaporated. 
Sachs8  found  that  from  a  surface  of  sunflower  stem  and  leaf  meas- 
uring 4, 920  centimeters  enough  water  transpired  to  form  a  layer 
2.23  mm.  thick  over  the  same  surface  ;   while  from  an  equal  sur- 
face of  water  enough  evaporated  to  lower  the  level  5.3  mm. 

Sachs  also  found  that  the  evaporation  from  an  animal  mem- 
brane is  greater  than  that  from  an  equal  surface  of  free  water. 
When  a  surface  of  water  is  covered  by  a  moist  layer  of  vegetable 
parchment,  evaporation  is  somewhat  retarded  ; 4  but  even  then  it 
is  greater  than  that  from  an  equal  surface  of  leaves. 

But  the  area  of  a  leaf  does  not  express  its  evaporating  sur- 
face, since  the  latter  consists  of  intercellular  spaces  which  have 
been  estimated  to  bear  the  ratio  of  ten  to  one  to  the  cuticularized 
exterior.  In  the  intercellular  spaces  the  air  is  saturated  with 
moisture,  hence  the  slowness  of  the  rate  of  transpiration.6 

739.  Effect  of  moisture  in  the  air  upon  transpiration.     All  ex- 
periments show  that  with  increase  in  the  amount  of  aqueous 
vapor  contained  in  the  air  the  amount  of  water  transpired  from 

1  Ann.  des.  Sc.  nat.,  ser.  3,  tome  xiii.,  1849,  p.  321.     Bonnet's  early  ex- 
periments are  interesting. 

2  Sitzungsh.  d.  Wiener  Akad.,  Bd.  xliv.,  Abth.  2,  1861,  p.  206. 
8  Handbuch  der  Experimental-physiologic,  1865,  p.  231. 

*  Baranetzky :  Botanische  Zeitung,  1872,  p.  65. 
6  American  Naturalist,  1881,  p.  385. 


276      TRANSFER   OF    WAT  Kit   THROUGH  THE    PLANT. 


a  plant  exposed  to  it  diminishes.1  When  the  air  is  completely 
saturated,  a  slight  amount  of  transpiration  can  take  place,2 
which,  as  Sachs  has  pointed  out,8  is  probably  due  to  the  fact 
that  the  temperature  of  the  plant  is  higher  than  that  of  the 
surrounding  air. 

740.  Instructive  experiments  upon  the  exhalation  of  moisture 
by  some  of  the  more  common  desert  plants  in  the  dry  air  of  the 
Western  plains  have  been  made  by  Sereno  Watson,4  from  which 
it  appears  that  in  about  four  hours  young  shoots  furnished  with 
about  fifty  per  cent  of  leaves  lost,  when  severed  from  the  stem, 
water  amounting  to  nearly  half  their  weight. 

741.  Effect  of  the  soil  upon  transpiration.    The  physical  prop- 
erties of  the  soil  have  an  influence  upon  transpiration.     Sachs5 
cultivated  plants  of  tobacco  in  clay  and  in  sandy  soil,  and  ob- 
served the  amount  of  water  transpired  by  them  under  like  con- 
ditions.     Although   his  experiments  are   not  conclusive,   they 
indicate  that  transpiration  is   more   uniform   from  the  foliage 
of  the  plants   grown  in  clay  than  from  the  plants   grown  in 
sand ;  the  former  soil  is  much  more  retentive  of  moisture,  and 
thus  the  supply  of  hygroscopic  water  is  given  up  more  gradually 
to  the  roots  of  the  plant. 

The  chemical  properties  of  soils  affect  transpiration  to  a  cer- 
tain extent.  Senebier,  in  1800,  stated  that  acids  increase  the 
rate  of  transpiration,  and  he  ascribed  the  same  effect  also  to 


1  The  relations  between  humidity  of  the  air  and  transpiration  are  shown 
by  the  results  obtained  by  linger  with  two  plants  of  Ricinus,  one  of  which 
was  in  the  open  air,  the  other  under  a  bell-jar.  (The  leaf  surface  of  one  plant 
was  190,  and  that  of  the  other  160  square  centimeters  ;  but  in  the  table  a  cor- 
rection has  been  made  so  that  equal  surfaces  are  compared). 


Duration  of  the  Experiment. 

Loss  of  water, 
open  air. 

Loss  of  water, 
bell-jar. 

Temperature  of 
the  air  in  C°. 

July  19  to  20  
"    20  to  21  
"    21to22  ,v. 

11.60  cc. 
17.05  " 
16.77   " 

1.60  cc. 
1.14  " 
1.55  " 

16. 
13.6 

15.4 

Total  

46.42  cc. 

4.35  cc. 

The  total  losses  bear  a  ratio  of  10.44  :  1. 

2  Handbuch  der  Experimental-physiologic,  1865,  p.  227.  Deherain  in 
Comptes  Rendus,  Ixix.  p.  381. 

8  Sitzungsber.  d.  Wiener  Akad.,  Bd.  xxvi.,  1857,  p.  326. 

*  Report  of  the  Geological  Exploration  of  the  Fortieth  Parallel,  Botany 
(1871),  p.  1. 

6  Versuchs-Stationen,  1859,  p.  232. 


EFFECT   OF    HEAT   UPON    TRANSPIRATION.  277 

alkalies.  But  as  Sachs1  showed  in  1859,  even  a  very  little  free 
acid  in  water  hastens,  while  an  alkali  retards,  transpiration. 

Burgerstein2  in  a  long  series  of  experiments  showed  that 
while  a  single  salt  added  to  water  in  less  amount  than  .5  per 
cent  hastens  transpiration,  any  per  cent  above  this  produces  a 
marked  retardation.  When  a  solution  of  nutrient  salts  is  used, 
even  if  its  concentration  is  as  low  as  .05  of  solid  matter,  there 
is  a  retardation,  and  this  is  greater  when  the  solution  is  more 
concentrated. 

In  the  experiments,  the  results  of  which  are  given  below, 
four  plants  of  Indian  corn  were  employed.  The  temperature 
varied  between  16.7°,  and  18°  C.,  and  the  observations  con- 
tinued through  one  hundred  and  three  hours.  The  amounts 
transpired  are  given  in  percentages  of  the  weight  of  the  fresh 
plants. 

Nutrient  solution 247.4 

Distilled  water 264.17 

Potassic  nitrate 283.2 

Ammonic  nitrate 334.2 

742.  Temperature  and  transpiration.     Rise  of  temperature  in- 
creases the  rate  of  transpiration  not  only  by  affecting  evaporation 
in  general,  but  indirectly  also  b}*  augmenting  the  absorption  of 
water  and  heightening  the  turgescence  of  the  cells.      Burger- 
stein   shows  that  leafy  twigs  of  yew  can  transpire  even  at  a 
temperature  of  — 10.7°  C.,  while  the   leafless  shoots  of  horse- 
chestnut  are  said  by  Wiesner  to  transpire  at  — 13°  C.3 

Sudden  changes  of  temperature  greatly  influence  transpiration, 
since  the  "  atmosphere  and  the  plant  cannot  follow  the  course 
of  temperature  with  equal  rapidit}-,  and  a  rarefication  of  the 
air  saturated  with  moisture  within  the  plant  must  favor  its 
release." * 

743.  Effect  of  light  upon  transpiration.    Transpiration  goes  on 
more  rapidly  in  light  than  in  darkness,  even  when  the  tempera- 
ture in  darkness  is  somewhat  higher.      But  differences  in  the 
intensity  of  diffused  light  do  not  produce  very  marked  differences 
in  the  amount  of  transpiration.     "When,  however,  diffused  light 

1  Versuchs-Stationen,  i.,  1859,  p.  223. 

Sachs  met  with  some  anomalies  in  his  experiments,  in  one  case  finding  a 
noticeable  retardation  of  transpiration  upon  the  addition  of  an  acid. 

2  Sitzungsb.  d.  Wiener  Akad.,  1876  and  1878. 

8  Quoted  by  Pfeffer:  Pflanzenphysiologie,  i.,  1881,  p.  148. 
*  Pfeffer  :  Pflanzenphysiologie,  i.,  1881,  p.  148. 


278      TRANSFER   OF   WATER    THROUGH   THE    PLANT. 


is  replaced  by  direct  sunlight,  the  increase  in  transpiration  is 
striking.1 

744.  Effects  of  different  rays  upon  transpiration.     Wiesner's 
conclusions,2  based  on  a  study  of  transpiration  in  different  rays 
of  the  spectrum,  are  as  follows  :    (1)  the  presence  of  chlorophyll 
appreciably  increases   the  action  of  light  upon  transpiration ; 
(2)  it  is  the   rays   corresponding  to  the   absorption-bands   of 
chlorophyll,  and  not  the  most  luminous  rays,  which  cause  trans- 
piration ;    (3)  rays  which  have  passed  through  a  solution  of 
chlorophyll  have  only  a  feeble  effect  upon  the  process ;   (4)  the 
non-luminous  heat-rays  act  as  do  the  luminous  rays,  but  in  a 
less  marked  manner,  the  ultra-violet   chemical  ra}'s  have  sub- 
stantially no  effect ;   (5)  whatever  the  rays  are,  they  always  act 
by  elevating  the  temperature  of  the  tissues. 

745.  Effect  of  shock  upon  transpiration.8    According  to  Bara- 
netzky,4  shaking  a  plant  for  a  short  time  increases  transpiration 

1  As  shown  by  the  following  experiments  by  Wiesner  :  — 


Name  of  plant. 

In  darkness. 

In  diffused  day- 
light. 

In  sunlight. 

Zea  Mais,  etiolated     .    .    . 
Zea  Mais,  green  
Spartium  jnnceum  (flowers) 
Malva  arborea  (flowers)  .    . 

106  mg. 
97  " 
64  " 
23  " 

112  ing. 
114  " 
69  " 

28  " 

290  mg. 
786  " 
174  " 
70  «' 

The  amounts  of  water  are  calculated  for  a  surface  of  100  square  centimeters, 
and  for  one  hour.  But  it  is  not  perfectly  clear  to  what  the  special  action  of 
light  can  be  due.  The  increased  size  of  the  cleft  of  stomata  under  light  cannot 
account  for  all  cases  ;  for  according  to  Wiesner  young  maize  plants,  in  which 
the  transpiration  is  large,  have  their  stomata  closed. 

2  Annales  des  Sc.  nat.,  ser  6,  tome  iv.,  1877,  in  which  may  be  found  also  a 
note  upon  the  same  subject  by  Deherain. 

8  See  also  Herbert  Spencer's  Experiments,  on  page  263. 

4  Botanische  Zeitung,  1872,  p.  89. 

The  following  example  will  show  the  results  of  Baranetzky's  experiment 
upon  a  leafy  stem  of  Inula  Helenium. 


Time  (morning) 

State  of  plant. 

Transpiration 
in  grams. 

Air 

temperature  C°. 

Atmospheric 
moisture. 

7.40 

quiet. 





_ 

8.10 

" 

.60 

22.1 

76  per  cent. 

8.40 

shaken. 

.62 

22.2 

76 

9.10 

quiet. 

.68 

22.4 

76 

9.40 

** 

.47 

22.6 

76 

10.10 

« 

.55 

22.7 

77 

10.40 

" 

.64 

22.9 

76 

11.10 

shaken. 

.59 

231 

76 

11.40 

quiet. 

.45 

23.3 

75 

12.10 

" 

.62 

23.4 

76        " 

RELATION    OF    TRANSPIRATION    TO    ABSORPTION.     279 

appreciabl}' ;  if  the  plant  is  then  kept  at  rest,  the  rate  falls  be- 
low that  previous  to  the  shaking,  after  which  it  gradually  rises 
to  its  normal  point.  Even  a  sharp  single  shock  is  enough  to 
produce  some  effect  upon  transpiration,  but  the  shaking  must 
continue  at  least  a  second  in  order  to  change  the  rate  very  much. 
If,  however,  the  shaking  is  long  continued,  or  short  shakings 
are  often  repeated,  there  is  a  noticeable  diminution  in  the  rate. 
Baranetzky  attributes  the  heightening  of  the  rate  by  a  sudden 
shock  to  the  correspondingly  sudden  compression  of  the  inter- 
cellular spaces  and  the  consequent  renewal  of  the  air  therein 
contained ;  while  the  diminished  rate  which  follows  continued 
shaking  is  due  to  a  partial  closing  of  the  stomata  (see  also 
731). 

746.  Relation  of  age  of  leaves  to  transpiration.     According  to 
Deherain1  and  Hohnel,2  young  leaves  exhale  more  water  than 
older  leaves.     Experiments  were  made  by  the  former  upon  the 
upper,  middle,  and  lower  leaves  of  rye.     From  the  newly  devel- 
oped leaves  more  water  was  exhaled  than  from  the  middle,  and 
more  from  the  latter  than  from  those  farther  down  the  stem. 
Sachs 8   states  that  young  leaves  exhale  less  than  those  which 
are  fully  developed,  but  that  there  is  some  diminution  in  the 
case  of  old  leaves. 

747.  Under  external  conditions  which  are  as  nearly  uniform  as 
can  be  secured  there  are  variations  in  the  rate  of  transpiration 
not  yet  understood  ;  these  are  generally  referred  to  variations  in 
the  tension  of  tissues  (see  1025). 

748.  Be&^pn  of  transpiration  to  absorption.     It  is  plain  that 
transpiration  from  leaves  is  the  chief  cause  of  absorption  by 
the  roots  ;  but  it  has  been  shown  by  Vesque  4  that  these  two 
functions  are  not  necessarily  proportional.     According  to  him 
it  is  only  when  a  plant  is  subjected  to  uniform   conditions  of 
diffused  light,  and  a  moderate  amount  of  moisture  in  the  air, 
that  they  are  about  equal.     In  a  very  dry  air,  transpiration  in 
the  case  of  most  plants  far  exceeds  absorption  until  wilting 
comes  on.    When,  on  the  other  hand,  a  plant  is  withdrawn  from 
a  moderately  moist  air  and  placed  in  an  atmosphere  saturated 
with  moisture,  absorption  goes  on  for  a  time  more  rapidly  than 
transpiration,  but  both  become  soon  arrested. 

The  dependence  of  the  rate  of  absorption  upon  temperature 


1  Cours  de  Chimie  Agricole,  1873,  p.  178. 

2  Forschungen  auf  d.  Geb.  d.  Agrikulturphysik,  1878. 
8  Handbuch  der  Experimental-physiologie,  1865,  p.  22 
*  Annales  des  Sc.  nat.,  ser.  6,  tome  vi.,  1878,  p.  222. 


280      TRANSFER   OF     WATER   THROUGH   THE   PLANT. 

has  been  shown  by  many  investigators,  notably  by  Sachs,1  who 
found  that  well-rooted  and  full-leaved  plants  of  gourd  and 
tobacco  wilted  when  the  temperature  of  the  air  and  soil  ranged 
from  3.7°  to  5°  C.,  although  the  ground  was  plentifully  supplied 
with  water.  When  the  temperature  of  the  soil  became  higher, 
the  leaves  became  again  turgescent. 

Another  cause  which  may  disturb  the  relation  between  absorp- 
tion and  transpiration  is  found  in  the  diminished  conductivity  of 
woody  tissue  at  low  temperatures.2 

749.  Checks  upon  transpiration.  Among  the  more  obvious  adap- 
tations of  plants  to  dry  climates  are  :  (1)  reduction  of  foliage  to 
a  minimum,  as  in  the  case  of  condensed  stems  (see  Vol.  J.  p.  64) ; 
(2)  a  coriaceous  or  even  denser  texture  of  leaves  or  of  branches 
resembling  leaves,  such  as  phyllocladia  (Vol.  I.  p.  65)  ;  (3)  ver- 
tically placed  leaves  or  their  analogues,  phyllodia,  in  many  if 
not  most  of  which  the  structure  of  the  parenchyma  and  of  the 
epidermis  with  its  stomata  is  the  same  on  both  sides ;  hence 
the  sides  have  substantially  the  same  exposure  to  air,  and,  in 
the  compass  leaves,  to  light  as  well  (see  448).  Another  adap- 
tation has  been  pointed  out  by  Pfitzer8  and  by  Westermaier ;  * 
namely,  the  possession  of  an  epidermal  or  subepidermal  "water 
tissue,"  or  "  water-storing  tissue  "  (see  209). 

Leaves  provided  with  water-storing  tissue  show  the  effect  of 
drought  first  in  the  partial  collapse  of  these  cells,  their  radial 
walls  becoming  somewhat  undulate,  while  the  assimilating  cells 
remain  full  and  unchanged  in  form.  These  water-storing  cells 
lose  comparatively  little  water  by  transpiration  ;  the  water  which 
the}-  contain  is  given  up  as  required  to  the  assimilating  paren- 
chyma. When  a  fresh  supply  of  water  is  afforded  to  the 
collapsed  water-storing  tissue,  the  recovery  of  turgescence  is 
immediate.  Examples  are  found  in  the  following  among  many 
other  plants  :  Peperomia,  Tradescantia  discolor,  Ficus  elastica. 

In  numerous  succulents  the  vacuoles  of  the  assimilating  cells 
frequently  contain  a  thin  mucus,  from  which  water  evaporates 
only  slowly,  and  this  is  believed  to  play  an  important  part  in 
the  storage  of  water.8 

Botanische  Zeitung,  1860,  p.  124. 

Beitrage  zur  Theorie  des  Wurzeldruckes,  1877,  p.  38,  quoted  by  Pfeffer, 
Pflanzenphysiologie. 

Ueberdie  mehrschichtige  Epidermis,  Pringsheini'.sJahrb.,viii.,  1872,  p.  16. 

Ueber  Bau  und  Function  des  pflanzlichen  Haurgevvebesystenis,  ibid.,  xiv. 

Plants  which  are  peculiarly  adapted  to  dry  climates  are  termed  by 
De  Candolle  Xcrophilous.  Among  them  arc  found  many  Composite,  notable 


EFFECTS    OF   TRANSPIRATION. 


281 


750.  The  chief  effects  of  transpiration  upon  the  plant  are: 
(1)  the  transfer  of  dilute  solutions  of  mineral  matters  to  the 
cells  where  assimilation,  or  the  production  of  organic  matter, 
takes  place ;  (2)  the  concentration  of  these  dilute  solutions  by 
evaporation.  The  extent  to  which  such  concentration  must 
take  place  can  be  easily  inferred  from  the  large  amounts  of 
water  which  are  exhaled  from  some  common  plants  under  ordi- 
nary conditions  of  culture.  According  to  Haberlandt,1  the  total 
amount  of  water  exhaled  from  a  plant  of  Indian  corn  during 
173  days  of  growth  was  14  kilograms  ;  of  hemp  during  140  days, 
27  kilograms  ;  and  of  sunflower  during  the  same  period,  66  kilo- 
grams. Hohnel 2  estimates  the  amount  of  aqueous  vapor  given 
off  between  June  1st  and  December  1st,  by  a  hectar  of  beech 
forest  (the  trees  averaging  rather  more  than  one  hundred  years 
in  age),  to  be  between  2,400,000  and  3,500,000  kilograms. 
That  the  leaves  in  autumn  contain  more  ash  constituents  than 
in  spring,  appears  from  numerous  analyses,  of  which  a  few 
are  here  given  from  Storer's  compilation. 


Name  of  Plant. 

Time. 

Condition  of 
Dryness. 

Per  cent 
of  Ash. 

Analyst. 

Oak  

May 

Fresh. 

1.30 

Saussure. 

"    

Sept. 

" 

2.40 

11 

Mulberry  .     .     . 

April 

" 

2.15 

Pupils  of  Fresenius. 

"          ... 

Aug. 

« 

4.90 

"             " 

Beech    .... 

May 

Dried  at  100°  C. 

4.67 

Kissmiiller. 

.... 

Nov. 

" 

11.42 

" 

751.   Influence  of  transpiration  upon  the  air.     El  >er  mover3  has 
shown  that  in  the  course  of  the  year  the  absolute  humidity  in  the 


proportions  of  Labiatse,  Liliaceae,  Palmaceae,  Myrtaceae,  and  Euphorbiacese  ;  but 
the  most  characteristic  orders  are  Zygophyllacese,  Cactacese,  Mesembryanthe- 
macese,  Cycadacese,  and  Proteacete  (Constitution  daiis  le  regne  vegetal  de 
groupes  physiologiques,  Arch.  Bibliotheque  universelle,  1.,  1874). 

1  Wissensch.-prakt.  Untersuchungen,  1877,  Bd.  ii. ,  p.  158. 

2  Ueber  die  Transpirationsgrosse  d.  forstl.  Holzgewachse,  1879,  p.  42.    Both 
this  and  the  preceding  citation  are  from  Pfeffer's  Pflanzenphysiologie,  i.  p.  153. 

"  Some  of  Haberlandt's  figures  for  crops  are  obviously  too  high,  probably 
from  overlooking  the  diminution  in  the  rate  of  transpiration  which  attends 
crowding  plants  together.  Thus  he  makes  the  total  amount  of  water  exhaled 
from  an  hectar  of  oats  during  the  period  of  vegetation  to  be  2,277,760  kg.  ;  of 
barley,  1,236,710  kg." 

8  Die  physikalischen  Einwirkungen  des  Waldes  auf  Luft  und  Boden,  1873, 
p.  148. 


282      TRANSFER   OF    WATER    THROUGH    THE    PLANT. 

air  of  a  forest  is  scarcely  greater  than  that  in  air  over  open 
ground.  But  the  relative  humidity  in  the  former  case  is  about 
six  per  cent  greater  than  that  in  the  latter. 

752.  It  has  been  held  by  many  that  forests  have  a  direct  effect 
in  increasing  the  amount  of  rain-fall,  presumably  by  bringing, 
through  transpiration,  the  amount  of  moisture  in  the  atmosphere 
of  a  wooded  place  nearer  the  point  of  precipitation.      But  the 
weight  of  evidence  now  available  is  against  this  view.1 

753.  On  account  of  the  shelter  which  they  afford,  the  trees  of 
a  forest  play  an  important  part  in  the  storage  of  a  water-supply. 
Under  their  branches  small  plants  can  thrive,  and  by  their  hold 
upon  the  ground  impart  to  even  very  porous  soil  a  good  degree 
of  stability. 

Soil  covered  with  mosses  and  other  humble  plants  which  live 
in  the  shade  not  only  holds  back  a  large  part  of  any  given  rain, 
so  that  the  water  drains  off  more  slowly,  but  it  is  not  likely  to 
be  itself  washed  down  to  lower  levels.  Upon  a  treeless  slope, 
however,  the  rains  which  fall  sweep  down  at  once. 

754.  There   is,    furthermore,   less   evaporation    from   a   soil 
covered  by  a  growth  of  trees  than  from  open  ground.     Obser- 
vations during  the   summer  months   recorded  by  Ebermeyer2 
show  that  the  evaporation  of  water  from  the  soil  of  a  forest, 
when  the  surface  is  not  covered  b}T  grass,  is  only  sixt}r-two  per 
cent  of  that  which  takes  place  from  open  ground.    But  if  the  soil 
under  the  shade  of  a  forest  is  covered  with  grass,  the  evaporation 
is  eighty-five  per  cent  of  that  in  the  open  ground. 

Von  Mathieu  found  that  the  evaporation  from  open  ground 
from  April  to  October  was  about  five  times  as  much  as  from 
wooded  soil ;  but  he  does  not  state  whether  the  soil  in  the  latter 
case  had  grass  upon  it  or  not. 

1  "Forests  increase  the  annual  relative  moisture  of  the  air,  but  this  in- 
fluence is  much  more  noticeable  at  high  elevations  than  at  low  elevations. 
The  precipitation  of  moisture  (dew,  cloud,  rain,  snow)  takes  place  more  readily 
on  this  account  in  wooded  than  in  treeless  regions,  and  the  frequency  and 
intensity  of  these  precipitations  increase  with  elevation  above  the  surface  of 
the  sea.     Moisture  descends  more  readily  and  frequently  upon  a  wooded  than 
upon  a  treeless  mountain  of  the  same  height.     Forests  affect  rain-fall  only  so 
far  as  they  increase  the  relative  amount  of  water  held  in  the  air,  and  thus 
bring  the  relative  amount  nearer  the  point  of  saturation  ;   thus  with  the  fall  of 
temperature  in  the  forest,  a  part  of  the  moisture  is  easily  precipitated.  .  .  . 
Forests  make  the  climate  of  a  country  moister,  and  especially  so  in  summer  " 
(Ebermeyer  :    Die   physikalischen   Einwirkungen   des  Waldes  auf  Luft  und 
Boden,  1873,  p.  151). 

2  Die  physikalischen  Einwirkungen  des  Waldes,  p.  175. 


EFFECTS   OF   TRANSPIRATION.  283 

755.  Effect  of  transpiration  upon  the  soil.      The  amount  of 
water  taken  from  the  soil  by  the  trees  of  a  forest  and  passed  into 
the  air  by  transpiration  is  not  as  large  as  that  accumulated  in  the 
soil  by  the  diminished  evaporation  under  the  branches.     Hence 
there  is  an  accumulation  of  water  in  the  shade  of  forests  which 
is  released  slowly  by  drainage.     But  if  the  trees  are  so  scattered 
as  not  materially  to  reduce  evaporation  from  the  ground,  the 
effect  of  transpiration  in  diminishing  the  moisture  of  the  soil  is 
readily  shown.     It  is  noted  especially  in  case  of  large  plants 
having  a  great  extent  of  exhaling  surface,  such,  for  instance, 
as  the  common  sunflower.     Among  the  plants  which  have  been 
successfully  employed  in  the  drainage  of  marsh}7  soil  by  transpi- 
ration probably  the  species  of  Eucalyptus l  (notably  E.  globulus) 
are  most  efficient. 

756.  Do  leaves  absorb  aqueous  vapor?   It  is  everywhere  known 
that  leaves  which  wilt  during  the  daytime  from  slight  dryness 
of  the  soil  may  recover  their  turgescence  during  the  night,  for 
then  transpiration  is  reduced  to  a  minimum,  and  the  demand  for 
water  is  very  slight,  so  that  there  is  a  speedy  readjustment  of 
the  equilibrium  which  was  disturbed  during  the  da}r.     It  is  still 
a  disputed  point  whether  wilted  leaves  can  absorb  any  appre- 
ciable amount  of  water  from  the  dew  which  falls  upon  them. 
Experiments  by  Duchartre2  indicate  that  the  amount  must  be 
very  small,  if  indeed  any  at  all.     That  leafy  branches  detached 
from  the  plant  can   absorb  water  through   the   leaves   is  well 
known,  and  has  been  already  alluded  to. 

1  See  a  very  interesting  account  by  Mueller  in   Eucalyptographia,  1881. 
Also  an  article  by  H.  N.  Draper  in  Chambers's  Journal,  Iviii.  193,  reprinted 
in  Littell's  Living  Age,  cxlix.  376. 

2  Ann.  des  Sc.  uat.,  ser.  4,  tome  xv.,  1861,  p.  109. 


CHAPTER  X. 

ASSIMILATION  IN   ITS   WIDEST   SENSE,  APPROPRIATION   OF 
CARBON,  NITROGEN,  SULPHUR,  AND  ORGANIC  MATTERS. 

757.  THE  term  assimilation,  as  generally  understood  in  Vege- 
table Physiology,   means  the  conversion  by  the  plant,  through 
the   agency  of  chlorophyll,  of  certain  inorganic  matters  into 
organic  substance. 

Some  authors,  however,  give  to  the  word  assimilation  a  wider 
signification,  namely,  the  conversion  into  utilizable  substance 
of  all  matters  whatsoever  brought  into  the  organism.  Such1 
regard  chlorophyll  assimilation  as  only  a  special  case  under  a 
general  class  which  comprises  the  appropriation  of  (1)  carbon, 
(2)  nitrogen,  (3)  sulphur,  so  far  as  this  is  a  constituent  of 
protoplasm,  (4)  certain  organic  matters. 

758.  It  will  presently  be  seen  that  with  the  appropriation  of 
carbon  by  the  plant,  there  is  always  associated  the  appropriation 
of  the  elements  of  water,  namely,  hydrogen  and  oxygen  ;  but  the 
mere  entrance,  transfer,  and  exit  of  water,  which  is  known  to 
undergo  no  chemical  change  in  the  organism,  have  already  been 
examined  in  Chapters  VII.  and  IX.,  and  do  not  strictly  belong  to 
the  process  of  assimilation.     There  are  sundry  mineral  matters 
which,  though  absolutely  essential  to  the  well-being  of  the  plant, 
are  conveniently  examined  without  special  reference  to  assimi- 
lation, even  in  its  widest  sense.     Some  of  them,  like  the  salts  of 
potassium,  are  indispensable  to  the  process  of  assimilation;  but 
they  do  not  become  at  any  period  an  indispensable  part  of  the 
substance  of  the  plant.    In  the  case  of  sulphur,  however,  a  small 
amount  of  the  element  is  appropriated  by  the  plant  and  consti- 
tutes a  component  part  of  its  protoplasmic  matter.    The  matters 
which  by  their  temporary  presence  in  the  plant  contribute  to 
its  activities,  have  been  likened  to  the  absolutely  necessaiy  lu- 
bricants without  which  machinery  cannot  run  easily  or  perhaps 
at  all. 

1  See  Pfeffer's  Pflanzenphysiologie,  i.  186. 


ASSIMILATING   SYSTEM  OF   THE  PLANT.  285 


APPROPRIATION  OF  CARBON,  OR  ASSIMILATION 
PROPER. 

759.  The  appropriation  of  carbon,  and  its  combination  with 
the  elements  of  water,  is  by  far  the  most  striking  of  the  kinds  of 
assimilation  ;  and  since  it  underlies  to  a  certain  extent  the  forma- 
tion of  the  matter  with  which  nitrogen  and  sulphur  are  incorpo- 
rated to  constitute  the  living  substance,  it  may  well  lay  claim  to 
be  considered  assimilation  proper.    It  was  employed  in  this  sense 
by  Asa  Gray  in  1850,  in  the  second  edition  of  the  Text-book. 

For  brevity,  therefore,  the  term  assimilation  in  the  present 
section  will  be  made  to  refer  to  the  appropriation  of  carbon. 

760.  With  some  exceptions,  to  be  mentioned  later,  the  follow- 
ing statement  holds  good  for  all  plants :  assimilation  is  essen- 
tially a  process  of  reduction  in  which  the  inorganic  matters  are 
(1)  water  taken  from  the  soil,  and  (2)  carbonic  acid J  taken  from 
the  air ;  and  the  organic  substance  produced  from  these  is  some 
carbohydrate  which  contains  less  oxygen  than  the  two  together. 
Hence  in  assimilation  there  is,  with  the  evolution  of  oxygen, 
a  partial  reduction  of  the  inorganic  matters  employed  in  the 
process. 

761.  Assimilation  takes  place  only  under  the  following  condi- 
tions: (1)  The  assimilating  organ  must  contain  living  chlorophj'll 
or  its  equivalent ;  (2)  water  and  carbonic  acid  must  be  furnished 
in  proper  amount ;  (3)  rays  of  light  of  a  certain  character  must  act 
upon  the  organ ;  (4)  it  must  be  kept  at  a  certain  temperature, 
there  being  a  minimum  degree  of  heat  below  which,  and  a  maxi- 
mum degree  above  which,  no  assimilation  can  occur ;  (5)  a  minute 
amount  of  certain  inorganic  matters  other  than  those  named, 
notably  some  compound  of  potassium,  must  be  within  reach. 

762.  The  assimilating  system  of  the  plant.     All  cells  which  con- 
tain chlorophyll  or  its  equivalent,  and  which  admit  of  exposure 
to  the  sun's  rays,  constitute  the  assimilating  system  of  the  plant ; 
but  it  must  not  be  understood  that  they  perform  only  assimilative 
work.      In  the  simplest  vegetable  organisms  (unicellular  or  fila- 
mentous algae)  and  even  in  some  water  plants  of  the  higher 
grade   (Anacharis)  these  cells  are  at  one  and  the  same  time 
members  of  an  absorbing,  a  storing,  and  an  assimilative  sys- 
tem.   In  land  plants,  and  in  some  water  plants,  however,  certain 
cells  have  the  office  of  assimilation  as  their  special  and  dominant 

1  In  general  throughout  this  work,  the  term  carbonic  acid  will  be  employed, 
Instead  of  carbon  dioxide,  to  denote  C0a. 


286  ASSIMILATION. 

function.  These  cells  are  found  chiefly  in  expansions  upon  or  of 
the  axis  ;  of  course,  most  commonly  in  ordinary  leaves.  But  in 
many  cases  the  primary  axis  itself  and  the  secondary  and  other 
axes  (branches)  may  have  a  considerable  share  of  the  proper 
assimilating  tissue  of  the  plant.  In  some  instances,  for  exam- 
ple, in  solid-stemmed  and  fleshy  plants  (as  Cactacese),  the  whole 
assimilative  apparatus  is  to  be  found  on  the  surface  of  axial 
instead  of  foliar  organs  ;  and  the  same  is  true  of  certain  ligneous 
plants  specially  adapted  to  desert  conditions  (e.  g.,  Colletia). 

763.  The  development  of  the   assimilative   system    in  land 
plants  appears  to  have  been  controlled  by  two  opposed  factors  ; 
namely,  (1)  the  advantage  to  be  derived  from  exposure  to  air  and 
light,  and  (2)  the  disadvantage  consequent  upon  too  great  loss 
of  moisture  by  evaporation.    Even  the  most  superficial  examina- 
tion of  the  tropical  plants  cultivated  in  our  hot-houses  reveals 
the  striking  manner  in  which  a  balance  has  been  struck  between 
these  conflicting  influences :  the  plants  of  warm  jungles  (e.  g., 
Scitamineae)  having  broad  and  long  leaves  suited  to  a  humid 
atmosphere,  while  the  plants  of  parched  sands  (Cactaceae  and 
the  like)  are  characterized  by  some  protection  against  excessive 
evaporation.     In  both  these  extreme  cases  the  provision  for  a 
certain  amount  of  evaporation  is,  on   the  whole,   seen   to   be 
tributary  to  the   essential   work   of  all   green   tissue,  namely, 
assimilation. 

764.  Proper  exposure  of  the  assimilating  apparatus  of  a  plant 
to  light  is  secured  (1)  by  the  shape  and  position  of  the  assimilat- 
ing organ,  whether  it  be  axis  or  leaf,  and  ('2)  by  the  arrangement 
in  the  organs  of  the  cells  themselves.     Concerning  the  first,  see 
Volume  I. ;  in  regard  to  the  second,  see  this  volume,  page  159. 

765.  Chlorophyll ]  (^Xwpos,  green,  and  <£u'AAov,  leaf).    The  term 
chlorophyll,  originally  applied  to  the  pigment  rather  than  to  the 
substance  which  contains  it,  is  now  used  indifferently  to  denote 
the  coloring-matter  and  the  portions  of  protoplasmic  mass  which 
are  tinged  by  it.     It  is  better,  however,  to  designate  the  former 
chlorophyll  pigment,  the  latter,  chlorophyll  granules,  or  grains. 

766.  In  regard  to  the  genesis  of  the  chlorophyll   granules 
which  are  the  essential  constituent  of  the  assimilative  cells,  the 

1  "  Nous  n'avons  aucun  droit  pour  nommer  une  substance  connue  depuis 
longtemps,  et  a  1'histoire  de  laquelle  nous  n'avons  ajoute  que  quelques  faits  ; 
cependant  nous  proposerons,  sans  y  mettre  aucune  importance,  le  nom  de 
chlorophyle,  de  chloros,  couleur,  et  <j>6\\ov,  feuille;  ce  nom  indiquerait  le  r61e 
qu'elle  joue  dans  la  nature  "  (Pelletier  and  Caventou :  Journ.  de  Pharmacie, 
Ui.,  1817,  490), 


ORIGIN   OF   CHLOROPHYLL  GRANULES. 


287 


following  view l  appears  to  be  most  in  consonance  with  recent 
investigations.  Imbedded  in  the  protoplasm  at  every  growing 
point  there  are  peculiar  bodies  (plastids)  which  have  substan- 
tially the  same  characters  and  structure  as  the  protoplasm,  and 
are  more  or  less  clearly  differentiated  from  it  even  at  an  eariy 
period.  As  the  cells  which  develop  from  the  growing  point 
assume  the  different  characters  which  fit  them  for  special  ser- 
vice, for  example,  those  in  certain  tubers  and  roots  for  store- 
houses, those  in  leaves  for  assimilation,  and  those  in  some 
flowers  and  fruits  for  color,  their  plastids  may  likewise  assume 
special  characters.  Those  which  are  destined  for  the  store- 
houses become  leucoplastids,  or  starch-formers ;  those  in  green 
tissue,  chloroplastids  or  chloroph}-!!  granules ;  and  those  in  col- 
ored flowers  and  fruits,  chromoplastids.  As  might  be  expected 
from  their  common  origin,  the  plastids  which  under  one  set  of 
conditions  might  become  leucoplastids,  may,  under  another  set, 
become  chloroplastids,  etc. 

767.  The  recognition  of  this  view  regarding  the  origin  of 
chlorophyll  grains,  etc.,  although  it  is  as  }ret  parti}'  hypotheti- 
cal, will  enable  the  student  to  explain  some  of  the  extraordi- 
nary intermediate  forms  met  with  ;  for  instance,  those  where  the 

1  Meyer  (Das  Chlorophyllkorn,  1883,  and  Botanisclies  Centralblatt,  1882)  has 
reached  substantially  the  same  results  as  those  obtained  by  Schimper,  which  in 
the  account  above  given  have  been  presented  with  Schimper's  nomenclature. 
Meyer  employs,  however,  the  somewhat  different  terminology  given  below. 


Older  Nomenclature. 

Schimper. 

Meyer. 

Van  Tieghem. 

General 

Plastid. 

Trophoplast. 

Leucite. 

term. 

Colorless  protoplasmic 

Special 

granule. 

Leucoplastid. 

Anaplast. 

Leucite  proper. 

terms. 

Chlorophyll  granule. 

Chloroplastid. 

Autoplast. 

Chloroleucite. 

Color-granule. 

Chromoplastid. 

Chromoplast. 

Chromoleucite. 

For  a  fuller  account  of  the  views  of  Meyer  and  Schimper,  the  student  must 
consult  the  original  memoirs  in  Botanische  Zeitung,  1883,  or  an  excellent 
abstract  by  Bower  (Quarterly  Journal  of  Microscopical  Science,  1884). 

Schmitz  (Die  Chromatophoren  der  Algen,  1882)  has  described  at  great 
length  certain  structures  analogous  to  chlorophyll,  occurring  in  some  of  the 
lower  plants.  These  granular  bodies,  called  chromatophores,  possess  consider- 
able diversity  of  form,  but  all  agree  in  consisting  of  a  matrix  or  basis  penneated 
by  coloring-matter.  In  most  green  algse  there  are  also  found  one  or  more 
minute,  rounded,  granular,  colorless  bodies  embedded  in  the  chromatophore, 
known  as  pyrenoids.  These  are  frequently  associated  with  granules  of  starch. 
Chromatophores  are  believed  by  Schmitz  to  increase  only  by  the  process  of 
division ,  but  the  pyrenoids  either  by  division  or  by  fresh  formation. 


288  ASSIMILATION. 

plastids  of  one  sort  can  for  a  time  undertake  the  office  of  the 
plastids  of  another  sort.  It  explains,  partially  at  least,  the  in- 
trusion of  chlorophyll  grains  into  parts  of  the  plant  where  they 
do  not  seem  to  properly  belong,  and  accounts  for  some  of  the 
apparent  changes  which  they  may  subsequently  undergo. 

768.  According  to  the  early  investigations  of  the  subject,  the 
chlorophyll  granules  were  regarded   as  differentiations,  at  an 
early  stage  in  the  embryo  and  seedling,  from  a  mass  of  homo- 
geneous protoplasm :    according  to  the  present  view  the}'  are 
derivatives  by  division  from  pre-existing  plastids.1    When  devel- 
oped in  darkness,  they  are  pale  yellowish,  or  even  devoid  of  color. 
Plants  grown  in  the  dark  (compare  788)  become  green  upon 
exposure  to  the  light,  provided  they  are  not  at  the  same  time 
kept  too  cold.     The  minimum  temperature-  at  which  they  turn 
green  is  different  for  different  plants,  but  may  be  said  to  be 
in  general  not  far  from  6°  to  10°  C. 

Certain  Gymnosperms,  notably  seedlings  of  Abies  and  Pinus, 
develop  a  bright  green  color  in  the  deepest  darkness,  provided, 
as  before  stated,  the  temperature  is  not  below  a  certain  point. 

769.  Occurrence  of  the  chlorophyll  granules.    The  granules  are 
found  only  ver}r  sparingly  in  epidermis,  being  chiefly  confined  to 
the  guardian  cells  of  stomata.     They  occur  principally  in  paren- 
chyma cells,  immediately  below  the  epidermis,  and  seldom  out 
of  reach  of  the  light.     But  they  occur  also  in  a  few  deep-seated 
structures,  for  instance,  in  the  thick  cortex  of  some  ligneous 
plants,  and  in  the  tissues  of  not  a  few  embryos. 

770.  That  chlorophyll  granules  are  found  in  the  interior  of 
some  of  the  lower  animals  appears  reasonably  certain,  but  the 
green  matter  does  not  always  present  the  same  characters.     Ac- 
cording to  recent  authorities,  it  assumes  in  most  cases,  for  in- 
stance in  Spongilla  and  Hydra,  the  form  of  minute  granules.    The 
pigment  agrees  in  some  of  its  essential  properties  with  that  of 
ordinary  chlorophyll.2    In  some  cases  it  must  still  be  considered 
an  open  question  whether  the  granules  may  not  be  (or  at  least 
represent)  independent  organisms  dwelling  in  certain  cavities  of 

1  The  views  of  Gris  (Ann.  des  Sc.  nat.  hot.,  1857)  may  be  summarized  as 
follows :  The  granules  arise  by  differentiation  of  the  protoplasm  in  certain 
young  cells  into  two  portions ;   one  of  these  assumes  the  form  of  roundish 
or  lenticular  bodies  (the  proper  granules),  which  under  the  influence  of  light 
become  colored  green,  while  the  other  remains  as  a  matrix  in  which  they  are 
embedded. 

2  For  an  interesting  treatment  of  this  subject,  consult  Geddes:  Nature,  1882, 
and  Lankester,  Journal  of  the  Royal  Microscopical  Society,  1882,  p.  241. 


STRUCTURE   OP   CHLOROPHYLL   GRANULES. 


289 


these  lower  animals.    These  cases  of  possible  symbiosis  deserve 
and  are  receiving  careful  investigation. 

771.  Many  species  of  plants  derive  all  or  a  part  of  the  organic 
matter  required  for  their  growth  and  proper  activities  either  from 
other  plants  (when  they  are  called  parasites),  or  from  decaying 
organic  matters,  such  as  vegetable  mould  (when  they  are  called 
saprophytes).     In  the  tissues  of  a  few  such  plants  minute  traces 
of  chlorophyll  may  sometimes  be  detected. 

772.  Structure  of  chlorophyll  granules.     Under  a  moderately 
high  power  of  the  microscope  the  granules  appear  as  spheroidal l 
or  polyhedral  bodies,  apparently  homogeneous  in  structure,  hav- 
ing neither  vacuoles  nor  granular  matter.     By  the  action  of  cer- 
tain solvents  it  is  possible  to  remove  from  the  granule  the  pigment 
which    has   imparted 

to  it  its  characteristic 
color,  when  the  mass 
remains  without  any 
change  of  form. 
Hence  it  is  proper  to 
distinguish  between 
the  chlorophyll  pig- 
ment and  the  chloro- 
phyll granule,  each 
of  which  will  now 
be  considered.  A 
method  recently  dis- 
covered makes  it  pos- 
sible to  demonstrate 
the  peculiar  structure 
of  the  granules  with- 
out complete  removal 
of  the  pigment.  This 
method,  known  as 
Pringsheim's,2  depends  upon  the  action  of  dilute  hydrochloric 
acid  on  the  green  parts  of  plants.  When  a  thin  green  tissue, 

1  In  some  of  the  Thallophytes,  the  whole  or  nearly  the  whole  of  the  proto- 
plasmic mass  seems  to  be  evenly  colored,  presenting  the  appearance  of  colored 
spirals,  lamellae,  stellate  forms,  etc. ;  and  such  colored  masses  are  strictly  chloro- 
phyll bodies  (Die  Chromatophoren  der  Algen.     Fr.  Schmitz.     Bonn,  1882). 

2  Pringsheim's  Jahrb.,  xii.,  1879,  p.  289. 

FIG.  149.  Hypochlorin.  A,  a  cell  of  CEdogonium  treated  with  hydrochloric  acid  for 
a  few  hours;  K,  the  same  after  some  days:  C,  D,  E,  needle-like  forms;  F,  two  cells  of 
Drapernalrtia  kept  in  hydrochloric  acid  one  month;  Q,  cell  of  Anacharis  in  hydrochloric 
acid  after  five  months'  treatment.  (Pringsheim.) 

19 


290 


ASSIMILATION. 


for  instance  a  leaf  of  Vallisneria  or  of  Anacharis,  is  treated 
with  a  solution  of  one  part  of  concentrated  hydrochloric  acid 
in  four  parts  of  water,  the  first  change  observed  is  merety  a 
fading  of  the  green  color  of  the  granules  to  a  yellowish  or 
brown.  After  a  few  hours,  however,  upon  the  periphery  of  each 
granule  there  appears  a  small  rounded  mass  of  a  deep  brown 
color,  generally  keeping  much  the  shape  of  the  granule  from 
which  it  has  been  extruded.  Often  more  than  one  of  these 
masses  can  be  detected,  and  they  sometimes  assume  needle-like 
or  staff-like  shapes.  But,  whatever  their  form  may  be,  they 
carry  out  of  the  granule  all  of  the  coloring-matter,  and  leave  it 
as  a  honey-combed  mass  of  its  original  shape.  Similar  extrusion 
of  a  colored  mass  can  be  effected  b}'  the  action  of  the  vapor  of 
boiling  water,  or  even  by  immersion  in  boiling  water ;  bul  here 
the  change  is  produced  in  a  single  hour,  or  even  less  (in  some 
cases,  in  five  minutes).  When  much  starch  is  present  in  the 
chlorophyll  granules  there  is  general!}'  considerable  change  of 
outline  of  the  whole  mass,  and  more  or  less  breaking  down  of 
their  internal  structure.  The  nature  of  the  vehicle  which,  under 
the  action  of  hydrochloric  acid  or  moist  heat,  carries  out  of  the 
granule  all  of  the  coloring-matter,  will  be  referred  to  later,  under 
the  name  given  it  by  Pringsheim,  namely,  Hypochlorin. 

773.  The  mass  of  the  granule  is  left  by  this  removal  of  its 
coloring-matter,  as  a  spongy  body  of  about  the  original  shape 
of  the  granule.     This  spongy  stroma,  or  "  trabecular  mass,"  is 
plainly  different  from  the  granule  which  is  decolorized  by  the 
action  of  solvents,  for  example,  alcohol,  ether,  etc. ;  for  in  the 
latter  case  the  mass  appears  to  be  with  an  unbroken  contour, 
and  has  a  solid  structure. 

774.  The  chlorophyll  pigment  can  be  extracted,  although  with 
various  associated  waxy  and  fatty  matters,  by  alcohol  and  other 
solvents.     To  prepare  a  solution  of  the  pigment  for  a  study  of 
its  most  striking  properties,  fresh  leaves  should  be  bruised,  acted 
on  for  a  few  hours  in  the  dark  by  warm,  strong  alcohol,  and 
then,  without  exposure  to  bright  light,  the  liquid  should   be 
carefully  decanted.      It   is  not  difficult  to   separate   the  dark 
green  solution  into  two  distinct  colors  by  means  of  the  following 
methods :  — 

(1)  Fremy's  process.  One  volume  of  the  alcoholic  solution 
is  shaken  with  a  mixture  of  two  volumes  of  ether  and  one  of 
concentrated  hydrochloric  acid ;  after  standing  for  a  time,  its 
upper,  or  ether  layer,  is  yellow  (phylloxanthin  or  xanthophyll), 
while  its  lower,  or  acid  layer,  is  blue  or  greenish  blue  (phyllo- 


THE   CHLOROPHYLL   PIGMENT.  291 

cyanin).  If  considerable  alcohol  is  now  added,  and  the  mixture 
shaken,  the  liquid  again  becomes  thoroughly  mixed  and  of  a 
clear  green  color.  Fremy's  later  researches  have  led  him  to  re- 
gard the  so-called  phyllocyanin  as  realty  an  acid  (phyllocyanic), 
which  is  probably  combined  with  potassium,  and  the  salt  thus 
formed  mixed  with  phylloxanthin  to  form  the  green  coloring- 
matter  of  chlorophyll. 

(2)  Eraus's  process.  This  method  of  separating  the  two 
coloring-matters  is  based  on  the  action  of  benzol.  The  alcoholic 
solution  prepared  as  directed  on  page  290,  or,  much  better,  with 
alcohol  of  65  %,  is  shaken  with  about  twice  its  volume  of  benzol, 
or,  according  to  R.  Sachsse,  with  benzin  (sp.  gr.  .714).  After 
a  while  the  turbid  liquid  separates  into  a  benzol  layer  above, 
having  a  bluish-green  color,  and  an  alcohol  layer  below,  tinged 
yellow.  The  yellowish  pigment  is  called  by  Kraus,  xanthophyll, 
the  bluish-green,  kyanophyll.  According  to  Wiesner,  kyanophyll 
is  nearly  pure  chlorophyll  freed  from  its  associated  3rellow  pig- 
ment xanthophyll.  It  is  believed  by  many  that  the  yellow  pig- 
ment separated  by  this  process  is  identical  with  that  found  in 
plants  blanched  (etiolated)  in  darkness,  and  which  has  been 
called  etiolin. 

Different  methods  (some  of  which  are  noticed  briefly  in  the 
foot-notes  1 )  have  been  employed  for  the  isolation  of  the  pure 

1  (1 )  Berzelius  evaporates  the  alcoholic  extract  to  dryness,  and  after  treatment 
with  hydrochloric  acid  (sp.  gr.  1.14),  again  dissolves  it  in  alcohol.  He  then 
precipitates  with  water,  redissolves  the  precipitate  after  filtration,  and  lastly, 
by  acetic  acid,  precipitates  the  nearly  pure  pigment  (Aunalen  der  Chemie  und 
Pharmacie,  xxi.,  1837,  p.  257  ;  xxvii.,  1838,  p.  296.)  (2)  Fremy  throws  down 
from  its  alcoholic  solution,  by  use  of  either  aluminic  or  magnesic  hydrate,  all 
coloring-matter  ;  and  after  thoroughly  washing  the  precipitate  dissolves  it  in 
alcohol  (Comptes  Rendus,  1.,  1860,  p.  405 ;  Ixi.,  1865,  p.  188).  (3)  Hoppe-Seyler 
first  extracts  all  waxy  matters  from  green  leaves  by  repeatedly  washing  them 
with  cold  ether,  and  then  treats  the  leaves  with  boiling  absolute  alcohol.  After 
the  alcoholic  solution  has  been  cooled,  again  heated,  and  allowed  to  stand,  red- 
dish crystals  (erythrophyll)  separate  from  it.  These  are  red  in  transmitted,  but 
green  or  whitish  in  reflected  light.  After  their  separation  the  residue  of  the 
solution  is  evaporated  to  dryness  and  again  dissolved  in  ether;  from  the  ether 
solution,  upon  slow  evaporation,  granules  are  thrown  down,  which  are  brown 
in  transmitted  and  green  in  reflected  light.  These  granules  may  be  obtained, 
by  repeated  solution  and  by  spontaneous  evaporation  of  the  solution,  in  the 
form  of  crystals  of  a  high  degree  of  purity,  which  are  called  by  Hoppe-Seyler 
chlorophyllan  (Zeitschr.  phys.  Chera.,  iii.  1879,  p.  339).  (4)  In  Gautier's  pro- 
cess, bruised  leaves  are  mixed  with  sodic  hydrate  and  pressed.  After  this  the 
residue  of  the  leaves  is  treated  with  alcohol  at  55°  C. ,  again  pressed,  and  then 
treated  with  cold  83  per  cent  alcohol,  all  waxy  matters  being  left  by  the  pro- 
cess undissolved.  The  alcoholic  solution  is  mixed  with  animal  charcoal  and 


292  ASSIMILATION, 

coloring-matters  of  leaves  :  crystalline  substances  have  been  ob- 
tained, one  of  which,  marked  by  its  blue  or  bluish-green  color, 
contains  about  five  per  cent  of  nitrogen.1 

775.  Spectrum  of  chlorophyll.     When  a  ray  of  white  light 
which  has  passed  through  a  coloring-matter,  for  instance,  a  solu- 
tion of  one  of  the  coal-tar  dyes,  red  wine,  or  a  solution  of  chlo- 
rophyll, is  examined  by  means  of  a  spectroscope,  certain  dark 
bands,  known  as  the  absorption-bands,  are  observed  at  definite 
places  in  its  spectrum. 

776.  For    convenience   in   examining  the   spectra   of   small 
amounts  of  coloring-matters,  a  direct- vision  spectroscope  attached 
to  the  tube  of  a  microscope  is  employed,  and  the  coloring-matter 
in  question  is  placed  in  a  flat-walled  bottle  or  a  glass  cell  on  the 
stage  of  the  microscope.     The  ray  of  light  which  is  reflected 
from  the  mirror  under  the  stage  passes  first  through  the  colored 
matter,  next  through  the  objective,  and  lastly  through  the  prisms 
which  compose  the  microspectroscopic  attachment  to  the  tube. 

777.  In  order  to  compare  the  spectra  of  different  substances; 
a  second  prism  or  set  of  prisms  is  often  used,  by  which  the  spec- 
trum of  a  second  liquid  can  be  projected  by  the  side  of  that  of 

allowed  to  stand  for  five  days  ;  all  the  chlorophyll  pigment  is  thus  removed  by 
the  charcoal.  Alcohol  of  65  per  cent  strength  extracts  from  the  coal  a  yellow 
crystallizable  substance,  while  ether  or  benzine  dissolves  out  matter  which, 
upon  evaporation  of  the  solution,  yields  pure  chlorophyll  pigment  (Comptes 
Rendus,  Ixxxix.,  1879,  p.  861).  By  the  action  of  sodium  on  a  benzine  solution 
of  the  coloring-matter  of  Primula  or  of  Allium,  R.  Sachsse  has  obtained  two 
colored  masses.  One  of  these  is  green,  solid  at  ordinary  temperatures,  in- 
soluble in  pure  water,  soluble  in  a  dilute  alkali,  and  also  in  alcohol  and  ether; 
the  other,  yellow,  brittle,  crumbling  into  an  orange  mass,  soluble  in  the  same 
liquids  as  the  first.  Besides  these  two  coloring  substances  he  found  also  a 
glucoside  (that  is,  a  body  which  under  certain  conditions  can  be  split  into 
some  one  of  the  sugars  and  another  substance  which  is  capable  of  further 
changes).  Both  of  the  colored  masses  can  be  readily  broken  up  into  several 
different  coloring-matters.  The  matters  obtained  by  this  process  from  the 
green  mass  differ  from  those  obtained  from  the  yellow,  in  containing  about 
three  to  five  per  cent  of  nitrogen,  while  those  from  the  yellow  contain  none 
at  all. 

1  The  green  crystals  obtained  by  the  evaporation  of  a  purified  solution  of 
chlorophyll  in  alcohol  are  called  chlorophyllan  by  Hoppe-Seyler,  and  chloro- 
phyll by  Gautier.     Their  analysis  reveals  the  following  composition :  — 
Hoppe-Seyler.  Gautier. 

C 73.345 73.97 

H 9.725 9.80 

0 9.525 10.33 

N 5.685 4.15 

Ash 1.73 1.75 


SPECTRUM  OP   CHLOROPHYLL.  293 

the  first.  The  spectra  of  chlorophyll  solutions  from  two  different 
sources  can  thus  be  at  once  compared.  One  of  the  combinations 
can  also  be  employed  to  project  the  solar  spectrum  (unchanged 
by  passing  through  any  color  whatever),  and  its  constant  lines 
(Fraunhofer's  lines)  can  be  used  for  the  determination  of  posi- 
tion of  the  bands  seen  in  the  spectrum  of  the  liquid  by  its  side. 

778.  The  spectra  of  many  substances,  among  which  chloro- 
phyll occupies  a  prominent  place,  have  absorption-bands  of  such 
constancy  in  position  and  appearance  that  they  are  justly  regarded 
as  characteristic. 

779.  The  spectrum  of  an  alcoholic  solution  of  chlorophyll  has 
been  shown  to  be  essentially  the  same  as  that  of  the  chlorophyll 
granule  itself.     In  order,  however,  to  obtain  all  the  absorption- 
bands  characteristic  of  chlorophyll,  it  is  necessary  to  examine 
successively  solutions  of  different  degrees  of  strength,  some  of 
the  bands  appearing  only  in  dilute  and  others  only  in  strong 
solutions.     For  comparison,   absorption  spectra  obtained  from 
different  sources  are  here  given. 


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150 

FIG.  150.  Spectra  of  chlorophyll.  The  upper  figure  shows  the  spectrum  of  an  alco- 
holic solution  of  medium  concentration,  while  the  middle  figure  gives  all  the  absorption- 
bands  of  chlorophyll ;  those  on  the  right  as  shown  only  in  dilute  solutions.  The  lowest 
figure  exhibits  the  spectrum  of  a  living  leaf  of  Deutzia  scabra.  (Kraus.) 


294  ASSIMILATION. 

780.  The  fluorescence  of  chlorophyll  pigment  is  best  shown  by 
allowing  rays  of  light,  made  convergent  by  passing  through  a 
double  convex  lens,  to  fall  upon  the  surface  or  side  of  a  strong 
alcoholic  solution  of  chlorophyll.     The  color  at  the  focus  of  the 
lens  will  then  appear  blood-red,  but  by  transmitted  light  the  same 
solution  will  appear  dark  green.     By  fluorescence  is  meant  the 
property  possessed  by  certain  substances  of  diminishing  the  re- 
frangibility of  some  rays  of  light ;  in  the  case  of  chlorophyll  all 
the  rays  towards  the  violet  end  of  the  spectrum  are  made  to 
conform  in  refrangibility  to  those  near  the  red.     A  bright  solar 
spectrum l  cast  upon  the  side  of  a  flat  vessel  containing  a  solu- 
tion of  chlorophyll  appears  much  like  a  stripe  of  dull  red :  in 
this  red  stripe  are  bands  corresponding  in  their  position  to  the 
absorption-bands  of  chlorophyll.    If  the  blood-red  color  produced 
by  a  strong  light  falling  on  the  surface  of  a  concentrated  solu- 
tion of  chlorophyll  is  examined  through  a  spectroscope,  only 
red  rays  having  the  same  degree  of  refrangibility  as  those  of 
the  deep  absorption-band  of  the  chlorophyll  spectrum  come  to 
the  eye. 

781.  Plants  without  chlorophyll.     If  whole   plants    (certain 
parasites  and  saprophytes,  for  example,  Monotropa)  are  either 
white  or  slightly  tawny  throughout,  it  is  owing  to  a  complete  or 
partial  absence  of  chlorophyll ;  but  in  some  instances  such  plants 
may  impart  to  alcohol,  in  which  they  are  immersed,  a  decided 
tinge,  frequently  blue. 

782.  " Colored"  plants.     When  leaves  or  stems  have  some 
color  other  than  green,  they  are  said  to  be  colored ;  if  two  or 
more  different  colors  are  intermingled  the  parts  are  variegated. 

783.  In  the  case  of  healthy  leaves  exposed  to  light,   white 
spots,  streaks,  etc.,  are  generally,  if  not  always,  characterized 
by  an  absence  of  chlorophyll.    Such  spots  have  relations  to  their 
surroundings  which  are  different  from  those  of  the  contiguous 
green  parts ;  the)-  do  not  have  the  power  of  assimilating  in- 
organic matters. 

784.  In  plants,  the  paleness  of  colors  verging  upon  green  or 
blue  (for  example,  those  in  many  kinds  of  cabbage)  sometimes 
depends  wholly  on  the  existence  upon  the  surface  of  the  part,  of  a 
great  amount  of  the  waxy  matters  known  collectively  as  bloom 
(see  226).    The  tissues  beneath  the  surface  may  be  vivid  green. 

785.  Red  and  yellow  colors  of  healthy  and  vigorous  leaves  are 
usually  due  to  the  presence  in  the  cells  (often  merely  those  of 

i  Hagenbach:  Annalen  der  Physik  und  Chemie,  cxlL,  1870,  p.  245. 


ETIOLATION.  295 

the  epidermis)  of  colored  cell-sap.  This  is  sometimes  in  such 
large  amount  as  to  mask  completely  the  green  granules  which 
are  contained  in  the  same  cells. 

786.  In  the  Florideae  (rose-red  marine  algae)  the  chlorophyll 
is  masked  by  the  presence  of  a  reddish  coloring-matter  which  is 
easily  extracted  by  pure  water.     This  reddish  pigment  is  called 
phycoerythrine.     In  solution  it  is  carmine-red  by  transmitted, 
and  orange  by  reflected  light.     Analogous  pigments  extracted 
by  water  from  algae  of  colors  other  than   red   have   received 
the  following  names,  —  phycophaeine  (brownish),  phycocyanine 
(bluish),  phycoxanthine  (yellowish-brown) . 

When  these  coloring-matters  have  been  extracted  by  cold 
water,  the  chlorophyll  is  left  unchanged  in  the  plant,  and  it 
then  imparts  to  the  thallus  its  characteristic  green  color.  Owing 
to  the  nearly  complete  insolubility  of  these  reddish  pigments  in 
alcohol,  and  the  complete  solubilitj'  of  the  chlorophyll  pigment 
in  that  liquid,  a  green  color  is  given  at  once  to  alcohol  when  an 
alga  is  immersed  therein. 

787.  Colored  bodies,  not  readily,  if  indeed  at  all,  distinguish- 
able from  ordinary  crystalloids  (see  177),  are  found  in  many 
algae.     In  some  cases  these  colored  granules  of  crystalline  form 
occur  normally  in  the  living  plant ;  in  others  they  arise  from 
changes  produced  by  the  action  of  reagents  upon  the  matters  of 
the  cells.     The  name  rhodospermin,   given  by  Cramer  to  the 
granules  having  the  latter  origin,  has  been  adopted  by  Klein  in 
an  extended  memoir. 

788.  Etiolation.     Green  plants  placed  in  darkness  soon  turn 
pale  and  become  blanched  or  etiolated.     The  chlorophyll  gran- 
ules change  their  color,  and  finally  appear  to  become  merged, 
with  more  or  less  change  of  form,  in  the  protoplasmic  mass, 
from  which  they  are  then  no  longer  easily  distinguishable.    Etio- 
lated pla.fts  when  exposed  to  light  recover  their  color  only  when 
the  temperature  is  above  a  certain  point.     The  action  of  light  in 
restoring  color  is,  moreover,  local,  being  confined  to  the  part  of 
the  plant  which  is  exposed  to  its  influence.     It  may  be  here 
noted  that  some  plants  are  not  etiolated  until  after  long  expos- 
ure to  darkness  ;  thus  the  older  parts  of  Cactus  speciosus,  kept 
in  the  dark,  remained  green  for  three  months,  but  the  new  shoots 
were  etiolated.      Selaginella  remained  green  from  four  to  five 
months.1 


1  Sachs  :  Handbuch  der  Experimental -physiologic,  1865;  also  Botanische 
Zeitung,  1864,  and  Flora,  1863. 


296 


ASSIMILATION. 


The  instructive  similarit}7  between  the  spectrum  of  the  yellow 
coloring-matter  of  chlorophyll  and  that  of  the  so-called  etiolin, 
or  yellow  coloring-matter  which  can  be  extracted  from  blanched 
leaves,  is  shown  in  the  two  figures  here  given. 


789.  An  alcoholic  solution  of  chlorophyll  undergoes  very  little 
if  any  change  when  kept  in  the  dark  ;  but  even  a  short  exposure 
to  strong  light  destroys  its  green  color,  and  leaves  the  liquid 
pale  brown,  or  nearly  colorless.     When,  however,  strong  sun- 
light passes  through  a  solution  of  chlorophyll  before  it  reaches  a 
second  receptacle  filled  with  the  same  liquid,  the  first  solution 
protects  the  second  for  a  considerable  time ;  and  only  after  the 
first  has  lost  a  portion  of  its  green  color  can  the  second  be  also 
acted  upon. 

790.  Sachs  l  has  pointed  out  the  interesting  fact  that  green 
leaves,  especially  those  of  delicate  texture,  become  paler  when 
exposed  to  a  very  bright  light,   and  resume  their  deep  green 
color  when  again  subjected  to  a  less  intense  light.     If  one  leaf 
is  partially  "shaded  by  another,  the  shaded  leaf  preserves  its  nor- 
mal deep  green  color,  while  the  leaf  exposed  to  the  light  grows 
distinctly  paler.     This  effect,  due  probably  to  a  change  of  posi- 
tion of  the  chlorophyll  grains,  can  be  shown   experimentally 
in  the  following  manner :   Fasten  closely  to  a  green  leaf,  still 

1  Ber.  iiber  die  Verhandlungen  (Math.  Phys.  Classe)  der  Siichsischen  Ge- 
sellsch.  xi.,  1859,  226;  and  also  in  Experimental-physiologic,  186o. 

FIG.  151.  The  upper  spectrum  is  that  of  the  yellow  constituent  of  chlorophyll  from 
Deutzia  scabra;  the  lower,  that  of  the  coloring-matter  of  etiolated  barley,  in  dilute 
solution.  (Kraus.) 


COLORS   OF  AUTUMN   LEAVES.  297 

connected  to  its  plant,  a  narrow  strip  of  flexible  lead  or  tin  foil, 
and  expose  the  leaf  to  bright  sunlight.  After  a  quarter  or  half  an 
hour  remove  the  strip,  and  the  spot  which  has  been  kept  shaded 
by  it  will  be  seen  to  be  distinctly  deeper  in  color  than  the  part 
which  has  been  exposed  to  the  sun's  rays. 

791.  Chlorosis,  or  blanching  of  plants   from  lack  of  iron. 
Although  iron  has  not  been  detected  as  a  constant  component 
of  the  pure  pigment  of  chlorophj-ll,  this  element  has  been  shown 
in  many  ways,  especially  by  water-culture,  to  be  essential  to 
the  green    color   and   even    to   the   normal   formation  of  the 
granules.        When  a   seedling   of  Indian   corn  is   grown  with 
its   roots   abundantly   supplied  with  a   nutrient   solution    from 
which  all  salts  of  iron  are  absent,  and  it  has  all  other  condi- 
tions favorable  to  rapid  and  healthy  development,  the  leaves 
are  pale  yellow,  or  even  whitish,  and  the  whole  plant  sooner 
or  later  appears  sickly  and  ill-nourished.      When,  however,  a 
salt  of  iron  is  supplied  to  the  nutrient  liquid,  a  normal  green 
color  is  at  once  imparted  to  the  leaves  and  the  plant  becomes 
healthy  and  vigorous.     The  effect  of  the  local  application  of  a 
salt  of  iron  is  thus  described :  When  a  weak  solution  of  ferric 
chloride,  ferric  nitrate,  or  ferrous  sulphate  is  applied  to  a  leaf 
blanched  by  want  of  iron,  the  part  moistened  assumes  a  nor- 
mal green  color  in  a  few  days,  and  sometimes  in  a  much  shorter 
period.     Neither  cobalt  nor  nickel  salts  have  similar  relations 
to  chlorophyll.1 

792.  Autumnal  changes  in  color.     The  leaves  of  many  decidu- 
ous plants  undergo  changes  of  color  at  some  period  before  they 
fall.     In  not  a  few  instances  these  changes  occur  early  in  the 
season  after  full  development  of  the  leaf;  for  example,  during 
the  first  days  of  summer  it  is  not  unusual  to  find  on  the  swamp 
maple  bright  red  and  yellow  leaves.     The  colors,  however,  be- 
come most  striking  in  temperate  climates  at  the  approach  of 
autumn. 

The  change  of  color  in  autumn  leaves  is  due  to  changes  which 
take  place  in  the  chlorophyll  pigment.  This  breaks  up  into 
various  matters  of  unknown  composition,  but  classed  in  a  gen- 
eral way  with  the  erythrophyll  (the  reddish  coloring-matter)  and 
xanthophyll  (the  yellowish),  obtainable  artificially  from  chloro- 
phyll. Comparison  of  the  spectra  of  these  substances  exhibits 
certain  very  striking  features  of  similar! t}r. 


1  Eusebe  Gris,  1844,  and  Arthur  Gris,  in  Ann.   des   Sc.  nat.,   ser.    4, 
tome  vii.,  1857,  p.  179. 


298 


ASSIMILATION. 


793.  These  autumnal  changes  have  been  compared,  not  in- 
aptly, to  those  belonging  to  the  ripening  process  in  colored  fruits  ; 
but  this  general  statement  of  similarity  must  not  disguise  the 
fact  that  in  the  ripening  of  fruits  special  chromoplastids  play  the 
chief  part,  whereas  in  the  leaf  before  its  fall  there  is  a  breaking 
up  of  the  protoplasmic  basis  of  the  granules  of  chlorophyll,1  pre- 
paratory to  the  withdrawal  from  the  leaves  into  the  plant  of  the 
useful  products  of  disintegration. 

The  changes  during  disintegration  may  involve  (1)  both  color 
and  form  of  the  granules  at  one  and  the  same  time,  or  (2)  the 
change  in  color  may  precede  that  in  form,  or  (3)  the  latter  may 
occur  first. 

794.  In  general,  the  reddish  coloring-matters  are  found  in  the 
cell-sap  of  the  colored  leaves,  the  yellow  in  the  substance  of  the 
disintegrating  grain,   and,   finally,   the  brown  in  the  modified 
character  of  the  cell-wall  itself. 

795.  That  frost  is  not  essential  to  the  production  of  the  leaf- 
colors  of  autumn  is  plain  from  the  widely  known  fact  that  many 
leaves  undergo  precisely  these  changes  of  color  long  before  any 
frosts  appear.     It  is  generally  believed,  however,  that  freezing 
may  somewhat  hasten  the  process  of  chlorophyll  disintegration 
which  underlies  all  the  changes. 

The  fact  is  generally  recognized  that  the  autumnal  colors, 
crimson  and  scarlet,  are  more  brilliant  in  the  cooler  portions  of 
America  than  those  which  characterize  the  foliage  in  Europe, 
and  it  has  even  been  remarked  that  the  leaves  of  American 
trees  cultivated  in  Europe  do  not  undergo  such  marked  changes 
of  color  as  individuals  of  the  same  species  do  in  their  native 
habitat.  This  has  been  accounted  for  on  the  ground  that  there 
is  less  humidity  in  the  atmosphere  of  eastern  America  ;  but  this 
explanation  is  not  satisfactory,  and  exact  observations  regarding 
the  relative  brilliancy  of  color  are  wholly  wanting. 

796.  Chlorophyll  in  evergreen  leaves.      At  the  approach  of 
cold  weather  the  leaves  of  evergreens  undergo,  according  to 
Mohl,2  certain  changes  of  color.     Kraus  8  recognizes  two  types 
of  change:   (1)  the  leaves  become  greenish  brown,  as  in  most 
Conifers,  or  (2)  they  take  on  a  red  color  on  the  upper  side,  as 
in  Mahonia  and  some  species  of  Sedum.     According  to  him,  in 
leaves  of  the  first  type  the  chlorophyll  granules  become  disinte- 


1  Sachs:  Die  Entleerung  der  Blatter  im  Hcrbst,  Flora,  1863,  p.  200. 

2  Vermischte  Schriften,  1845. 

*  Sitzungsb.  der  phys.-med.  Society  zu  Erlangen,  1871,  1872. 


AUTUMNAL  CHANGES   IN   LEAVES   OP   EVEEGREENS.     299 

grated  and  impart  a  brown  color  to  the  protoplasmic  mass  of  the 
cells ;  but  in  the  leaves  of  the  second  t3*pe  the  color  is  due  to 
a  highly  refractive  reddish  or  yellow  mass  (supposed  to  be  tan- 
nin), concealing  from  a  surface  view  the  clustered  chlorophyll 
granules  within,  which  retain  their  vivid  hue.  In  all  cases  of 
evergreen  leaves  the  granules  of  chlorophyll,  at  the  beginning 
of  the  cold  season,  pass  from  the  walls  to  the  centre  of  the  cells, 
and  are  there  aggregated  in  compact  clusters.  Their  normal 
condition  is  restored  in  the  warm  da3's  of  earl}"  spring. 

797.  Kraus  has  examined  the  changes  in  autumn  in  the  chloro- 
phyll of  Ruscus  aculeatus.    He  finds  that  in  this  plant  some  of  the 
more  superficial  cells  under  the  epidermis  contain  minute  granular 
masses  of  a  brownish  color,  but  no  chlorophyll  granules  are  to 
be  distinctly  seen,  and  that  the  subjacent  cells  have  more  or  less 
broken-down  granules  which  are  yellowish  or  brownish  green. 
In  the  cells  making  up  the  more  spongy  tissues  there  are  a  few 
chlorophyll  granules  quite  intact,  but  there  are  indications  that 
some  others  have  been  completely  destroyed  and  their  coloring- 
matter  taken  up  by  the  surrounding  protoplasm,  apparently  in  a 
state  of  solution. 

798.  It  was  thought  b}7  Kraus  that  the  winter  change  in  the 
character  of  the  chlorophyll  was  due  to  the  lower  temperature. 
He  based  his  views  largely  upon  experiments  with  a  branch  of 
Buxus  (Box)  ;  but  it  has  been  shown  by  Batalin 1  and  Askenasy 2 
that  light  has  a  more  important  influence  upon  the  chlorophyll 
than  changes  of  temperature. 

799.  The  raw  materials  required  for  assimilation,  and  their 
reception  by  the  assimilating  organs.     These  are  (1)  water  and 
(2)  carbonic  acid.      In  earlier  chapters  it  has  been  shown  in 
what  manner  and  to  what  extent  water  and  small  traces  of  min- 
eral matters  are  brought  from  the  soil  into  the  plant.      It  is 
now  necessary  to  ascertain  in  what  way  carbonic  acid  enters 
the  organism  and  is  appropriated  by  it. 

800.  Absorption  of  carbonic  acid  by  water  plants.     These  can 
absorb  carbonic  acid  substantially  as  they  absorb  mineral  salts, 
directly  from  the  water  in  which  they  live.     The  amount  of  car- 
bonic acid  found  in  rain  and  other  waters  is  variable,  ranging, 
according  to  the  best  authorities,  from  about  one  per  cent  to 
considerably  less  than  one  tenth  of  one  per  cent.     The  amount 
existing  in  the  free  state  in  natural  waters  in  which  plants  thrive 

1  Botanische  Zeitung,  1874. 
3  Botanische  Zeitung,  1875. 


300  ASSIMILATION. 

is  shown  in  the  following  table  (taken  from  the  comprehensive 
synopsis  in  Watts's  dictionary)  :  — 

Cubic  centimeters 
in  each  liter  of  water. 

Loch  Katrine  (Scotland) 3 

Bala  Lake  (Wales) 1.1 

Rhine  at  Strasburg 7.6 

Rhone  at  Geneva 8.4 

Thames  at  Kew 50.3 

All  the  free  carbonic  acid  dissolved  in  water  can  be  expelled 
"by  boiling.1 

801.  Absorption  of  carbonic  acid  by  land  plants.     These,  with 
their  foliage  exposed  to  the  air,  obtain  from  that  source  all  their 
supply  of  carbonic  acid.     No  carbonic  acid  is  taken  up  by  their 
roots  : 2  the  supply  enters  the  plant  through  the  younger  epider- 
mal tissues,  chiefly,  of  course,  that  of  the  leaves.    By  the  process 
of  respiration  within  the  plant  (see  Chapter  XI.)  a  small  but  ap- 
preciable amount  of  carbonic  acid  is  produced,  and  a  part  of  this 
is  doubtless  appropriated  directly  by  the  plant  for  the  process 
of  assimilation. 

802.  Carbonic  acid  and  other  gases  found  in  the  atmosphere 
sustain  to  vegetable  membranes  certain  relations  which  must 

1  According  to  Bunsen  (Jahresb.  der  Chemie,  1853,  p.  317),  one  volume  of 
water  absorbs  at  760  mm.  barometric  pressure,  and  at  the  temperatures  noted, 
the  following  amounts  of  various  gases  :  — 

3°.2C.  19°.6C. 

Nitrogen 02189  vol 01515  vol. 

Oxygen 04553    " 03253    " 

Carbonic  acid      .     .     1.5184      " 8545     " 

According  to  the  same  authority,  these  gases  occur  in  rain-water  in  the  fol- 
lowing relative  proportions  :  — 

0°C.  10°  O.  20°  C. 

Nitrogen  .  .  .  63.20  ...  63.49  ...  63.69 
Oxygen  ....  33.88  .  .  .  34.05  .  .  .  34.17 
Carbonic  acid  .  .  2.92  ...  2.46  ...  2.14 

2  This  appears  to  be  settled  by  the  results  of  experiments  made  by  Moll : 

( 1 )  when  carbonic  acid  is  afforded,  even  in  excess,  to  shoots,  whose  leaves  are  kept 
in  an  atmosphere  free  from  carbonic  acid,  no  formation  of  starch  takes  place  ; 

(2)  if  such  leaves  are  in  the  open  air,  the  formation  of  starch  is  not  increased 
above  its  normal  rate;  (3)  when  carbonic  acid  is  supplied  to  roots  of  plants 
whose  leaves  and  shoots  are  kept  in  an  atmosphere  free  from  carbonic  acid,  no 
formation  of  starch  takes  place.      If  the  leaves  and  shoots  of  such  plants 
are  in  the  open  air,  there  is  no  increase  of  starch  above  the  normal  amount 
(Arbeiten  des  bot.  Inst.  in  Wiirzburg,  1878,  p.  113). 


DIFFUSION   OF  GASES.  301 

now  be  presented  in  a  general  manner ;  and  some  introductory 
reference  must  be  here  made  to  the  well-known  physical  proper- 
ties of  gases.1 

803.  Diffusion  of  gases.    When  two  or  more  gases  are  brought 
into  contact,  spontaneous  intermixture  takes  place.     This  pro- 
cess of  diffusion,  as  it  is  called,  goes  on  even  when  the  gases 
are  very  different  in  specific  gravity,  and  when  they  are  kept 
externally  at  perfect  rest.     Thus  if  a  jar  of  carbonic  acid  be 
placed  in  connection  with  a  jar  of  oxygen,  the  two  gases,  after 
a  while,  will  become  uniformly  commingled. 

Similar  commingling  of  gases  also  takes  place  through  per- 
meable substances,  such  as  thin  plates  of  unglazed  porcelain, 
graphite,  films  of  membrane,  etc. 

804.  Different  gases  diffuse  through  a  given  membrane  in 
different  times.     The  rates  of  diffusion  of  different  gases  at  the 
same  temperature  and  barometric  pressure  have  been  shown  by 
Graham  to  differ  nearty  in  the  inverse  ratio  of  the  square  roots 
of  their  densities,  thus  :  — 


Name  of  gas. 
Hydrogen    .     . 
Carbonic  oxide 

Rate  of  diffusion 
(air  being  taken  as  unity). 

.     .     .     3.83     .     .     . 

1 

.     .     3.78  i 

icarly 

.     .     .     1.01  nearly   . 
1  01      " 

.     .     1.01 
.     .     1.01 
.     .       .95 
.     .       .81 

Oxygen  . 

.     .     .       .95     " 

Carbonic  acid  . 

.     .     .       .81     " 

1  Graham,  who  made  a  careful  study  of  the  laws  which  govern  gaseous  dif- 
fusion, has  given  the  following  clear  account  of  the  physical  hypothesis,  which 
is  now  generally  received  :  "  A  gas  is  represented  as  consisting  of  solid  and 
perfectly  elastic  spherical  particles  which  move  in  all  directions,  and  are  ani- 
mated with  different  degrees  of  velocity  in  different  gases.  Confined  in  a 
vessel,  the  moving  particles  are  constantly  impinging  against  its  sides  and  oc- 
casionally against  each  other,  and  this  contact  takes  place  without  any  loss  of 
motion  owing  to  the  perfect  elasticity  of  the  particles.  If  the  containing 
vessel  be  porous,  then  gas  is  projected  through  the  open  channels,  by  the 
motion  described,  and  escapes.  Simultaneously  the  external  air  is  carried 
inwards  in  the  same  manner  and  takes  the  place  of  the  gas  which  leaves  the 
vessel.  To  this  molecular  movement  is  due  the  elastic  force,  with  the  power 
to  resist  compression,  possessed  by  gases.  The  molecular  movement  is  acceler- 
ated by  heat  and  retarded  by  cold,  the  tension  of  the  gas  being  increased  in  the 
first  instance  and  diminished  in  the  second.  Even  when  the  same  gas  is 
present  both  without  and  within  the  vessel,  or  is  in  contact  with  both  sides 
of  our  porous  plate,  the  movement  is  sustained  without  abatement  —  molecules 
continuing  to  enter  and  leave  the  vessel  in  equal  number,  although  nothing 
of  the  kind  is  indicated  by  change  of  volume  or  otherwise.  If  the  gases  in 
communication  be  different,  but  possess  sensibly  the  same  specific  gravity 
and  molecular  velocity  as  nitrogen  and  carbonic  oxide  do,  an  interchange  of 


302 


ASSIMILATION. 


805.  The  movements  of  gases  within  the  plant  are  of  two 
kinds,  (1)  molecular  (see  note  on  the  previous  page),  and  (2) 
"the  movement  of  the  whole  mass  depending  exclusively  on 
expansive  force."     These  are  generally  conjoined  in  the  passage 
of  gases  through  the  plant. 

806.  Passage  of  gases  through  epidermis  free  from  stomata. 
The  assimilating  apparatus  in  ordinary  land  plants  consists  of 
parenchyma  cells  frequently  so  loosely  conjoined  as  to  have  very 
conspicuous  intercellular  passages,  which  communicate  with  sto- 
mata either  directly  or  indirectly.    All  of  these  pai'enclryma  cells 
have  walls  of  cellulose  generally  without  any  impregnation  of 
foreign  matter.     But  the  peripheral  cells  which  bound  the  whole 
as  epidermis  proper  are  cutinized  on  their  external  aspect,  and 
must  possess  relations  to  gases  different  from  those  presented  by 
common  parenchyma  with  uninfiltrated  walls. 

807.  Through  ordinary  cell-walls,  that  is,  those  which  are  com- 
posed of  nearly  pure  cellulose,  water  passes  and  gases  diffuse 
with  facilit\*.     But  as  cutinized  cell- walls,  like  those  of  the  epi- 
dermis of  leaves,  are  nearly  impervious  to  water  and  to  aqueous 
vapor,  it  would  at  first  sight  appear  unlikely  that  gases  could 
make  their  way  through  them  ;  such,  however,  is  not  the  case. 
Experiments  upon  epidermal  tissues  free  from  stomata  show 
that  under  ordinary  circumstances   gases  can  diffuse  through 
cutinized  walls. 

Thus  N.  J.  C.  Mtiller1  used  the  epidermis  of  the  leaves  of 
Haemanthus  puniceus  in  three  series  of  experiments  upon  the 
diffusion  of  different  gases.  The  membrane  employed  was,  in 
the  first  series,  two  films  of  epidermis  with  a  layer  of  water  be- 
tween them ;  in  the  second,  two  moist  films  without  any  layer 
of  water ;  in  the  third,  two  films  joined  together  and  then  care- 
fully dried  in  an  exsiccator  at  40°  C.  The  method  used  by 
Miiller  is  open  in  some  of  its  details  to  criticism,  but  in  a  general 
way  the  results  are  instructive.  The  following  are  the  mean 
ratios  indicating  the  rate  of  diffusion  obtained  :  — 


Series  I. 

Series  II. 

Series  III. 

Hydrogen    

100 

100 

100 

Oxygen  . 

502 

55 

37 

Nitrogen      
Carbonic  acid  

471 
687 

73 

48 

30 
45 

molecules  also  takes  place  without  any  change  in  volume.    With  gases  opposed 
of  unequal  density  and  molecular  velocity,  the  permeation  ceases,  of  course,  to 
be  equal  in  both  directions  "  (Philosophical  Transactions,  1863). 
1  Pringsheim's  Jahrb.,  1869,  p.  169. 


PASSAGE   OF    GASES   THROUGH   STOMATA.  303 

808.  Experiments  by  a  wholly  different  method  were  con- 
ducted b}'  Boussingault,1  upon  leaves  of  Oleander.     By  a  leaf 
having  an  upper  surface  of  37.2  square  centimeters  free  from 
stomata,  and  completely  closed  on  the  under  side  by  tallow, 
17.5  cubic  centimeters  of  carbonic  acid  were  absorbed  in  a  given 
time. 

In  another  series  of  experiments  Boussingault  fastened  the 
under  surfaces  of  two  leaves  closely  together  by  means  of  paste, 
so  that  only  the  upper  surfaces  (free  from  stomata)  were  exposed 
to  the  air ;  with  these  leaves  nearly  the  same  results  were  ob- 
tained as  in  the  first  series. 

809.  Passage  of  gases  through  stomata.     Stomata  (see  Figs. 
52  and  54)  are  practically  minute  apertures  in  thin  plates,  and 
under  ordinary  circumstances   there   is  no  obstruction   to   the 
ready  passage  of  gases  through  them  from  the  surroundings  into 
the  interior  of  the  plant.     The  changing  pressure  caused  by  agi- 
tation of  the  foliage  exerts,  as  it  does  in  aqueous  transpiration, 
an  important  influence  in  facilitating  this  passage. 

810.  Merget2  holds  that  it  is  chiefly  through  stomata  that 
the  interchange  of  gases  with  the  outer  air  takes  place  in  the 
plant ;  but,  on  the  other  hand,  it  is  claimed  by  Barthelemy 8  that 
they  play  only  a  very  subordinate  part.      There  can  be  little 
doubt  that  the  earlier  view  advanced  and  illustrated  by  Du- 
trochet,4  and  further  b}T  Garreau,6  is  substantially  correct ;  namel}r, 
that  gases  enter  and  escape  from  the  plant  freely  both  by  diffu- 
sion through  the  cuticularized  cell-walls  of  the  epidermis  and 
by  passage  through  the  stomata. 

811.  Atmospheric  air  is  chiefly  a  mixture  of  two  gases,  oxj'gen 
and  nitrogen.     The  proportions  in  which  these  substances  and 
others,  occurring  in  much  smaller  amounts,  are  found  in  dry  air 
are  usually  stated  as  follows  :  — 

Proportions  by  volume.  Proportions  by  weight. 

Nitrogen 79.01984  76.8399 

Oxygen 20.94000  23.1000 

Carbonic  acid 04000  .0600 

Ammonia  .00016  .0001 


100.  100. 


1  Agronomic,  iv.,  1868,  p.  374. 

2  Comptes  Rendus,  Ixxxiv.,  1877,  p.  376. 

Ann.  des  Sc.  nat.  hot.,  ser.  5,  tome  xix.,  1874,  p.  131. 
*  Ann.  des  Sc.  nat.,  tome  xxv.,  1832,  p.  242. 
6  Ann.  des  Sc.  nat.  hot.,  ser.  3,  tomes  xv.,  xvi. 


304  ASSIMILATION. 

The  first  two  substances  occur  in  very  nearly  the  same  pro- 
portions in  free  atmospheric  air  wherever  found,1  but  the  amounts 
of  the  last  two  vary  within  narrow  limits. 

Besides  the  foregoing  substances,  the  following  are  also  men- 
tioned as  having  been  found  in  dry  air  in  minute  traces  :  Nitric 
acid,  nitrous  acid,  ozone,  marsh  gas,  carbonic  oxide,  sulphurous, 
sulphydric,  and  hydrochloric  acids,  and  hydrogen. 

812.  Under  ordinary  circumstances   the   proportion  of  car- 
bonic acid  in  the  atmosphere  does  not  increase  much  beyond  the 
amount  stated  above,  namely,  four  one-hundredths,  or  one  twenty- 
fifth  of  one  per  cent.2    Pettenkofer  assigns  one  twentieth  of  one 
per  cent  as  the  amount  in  the  air  of  Munich  (1,690  feet  above 
the  level  of  the  .sea) . 

In  confined  spaces,  however,  the  accumulation  of  carbonic 
acid  (once  known  by  the  significant  term  fixed  air)  ma}'  be- 
come so  great  as  to  render  the  air  irrespirable.  It  was  the  con- 
sideration of  the  question  how  such  air  could  be  again  rendered 
fit  for  respiration  that  led  to  the  first  successful8  investigation  of 
the  action  of  plants  upon  the  atmosphere. 

813.  The  amount  of  carbonic  acid  found  in  ordinary  water 
which  has  been  exposed  for  a  time  to  the  air  is  sufficient  for  the 
supply  of  this  gas  to  water  plants.     The  percentage  of  the  gas 
in  the  atmosphere  under  ordinary  conditions  is  ample  for  all  the 
needs  of  land  plants.     The  consideration  of  the  effect  of  supply- 
ing a  larger  amount  than  usual  of  this  gas  to  water  and  laud 
plants,  in  order  thereby  to  influence  the  activity  of  the  assimila- 
tive process,  must  be  deferred  until  all  the  conditions  essential 
to  assimilation  have  been  considered ;   but  it  ma}-  be  said,  in 
passing,  that  any  large  excess  of  carbonic  acid  over  the  supply 
furnished  to  plants  in  nature  diminishes  assimilative  activity. 

1  For  a  very  instructive  summary  of  results  of  the  examination  of  the  air 
in  different  localities,  the  reader  should  consult  "Air  and  Rain,  the  Begin- 
nings of  a  Chemical  Climatology,"  by  E.  Angus  Smith  (London,  1872). 

8  Angus  Smith  gives  the  following  results  of  his  examination  in  1864  of  the 
air  of  Manchester,  England  :  — 

Per  cent  of  CO2  in  atmosphere. 

In  the  streets,  usual  weather 0403 

During  fogs 0679 

Where  the  fields  begin 0369 

In  close  buildings 1604 

Minimum  amount  found  in  suburbs 0291 

See  also  Ann.  de  Chimie  et  de  Physique,  1883,  for  reports  on  the  amount  of 
CO,  in  the  atmosphere  of  different  localities. 
«  See  the  historical  sketch,  pp.  323,  324. 


PRACTICAL   STUDY.  305 

814.  Practical  study  of  assimilation.  Before  examining  the 
remaining  conditions  of  assimilation,  a  simple  experiment  is  here 
described  03-  which  the  reader  can  study  in  their  proper  relations 
all  the  essential  conditions  of  the  process,  and  thus  obtain  a 
clearer  idea  of  the  means  by  which  the  activity  of  assimilation 
is  measured  and  the  indispensable  character  of  the  conditions 
established. 

Fill  a  five-inch  test-tube,  provided  with  a  foot,  with  fresh  drink- 
Ing  water.  In  this  place  a  sprig  of  one  of  the  following  water 
plants,  —  Anacharis  Canadensis,  Myriophyllum  spicatum,  M. 
verticillatum,  or  any  leafy  Myriophyllum  (in  fact,  any  small- 
leaved  water  plant  with  rather  crowded  foliage).  This  sprig 
should  be  prepared  as  follows :  Cut  the  stem  squarely  off,  four 
inches  or  so  from  the  tip,  dry  the  cut  surface  quickly  with 
blotting-paper,  then  cover  the  end  of  the  stem  with  a  quickly 
drying  varnish,  for  instance  asphalt-varnish  (see  115),  and  let 
it  dry  perfectly,  keeping  the  rest  of  the  stem  if  possible  moist  by 
means  of  a  wet  cloth.  When  the  varnish  is  dry,  puncture  it  by 
a  needle,  and  immerse  the  stem  in  the  water  in  the  test-tube, 
keeping  the  varnished  larger  end  uppermost.  If  the  submerged 
plant  be  now  exposed  to  the  strong  rays  of  the  sun,  bubbles  of 
oxygen  gas  will  begin  to  pass  off  at  an  even  and  rapid  rate,  but 
not  too  fast  to  be  easily  counted.  If  the  simple  apparatus  has 
begun  to  give  off  a  regular  succession  of  small  bubbles,  the  fol- 
lowing experiments  can  be  at  once  conducted. 

(1)  Substitute  for  the  fresh  water  some  which  has  been  boiled 
a  few  minutes  before,  and  then  allowed  to  completely  cool :  by 
the  boiling,  all  the  carbonic  acid  has  been  expelled.    If  the  plant 
is  immersed  in  this  water  and  exposed  to  the  sun's  rays,  no  bub- 
bles will  be  evolved ;  there  is  no  carbonic  acid  within  reach  of 
the  plant  for  the  assimilative  process.     But, 

(2)  If  breath  from  the  lungs  be  passed  b}-  means  of  a  slender 
glass  tube  through  the  water,  a  part  of  the  carbonic  acid  exhaled 
from  the  lungs  will  be  dissolved  in  it,  and  with  this  supply  of 
the  gas  the  plant  begins  the  work  of  assimilation  immediately. 

(3)  If  the  light  be  shut  off,  the  evolution  of  bubbles  will  pres- 
ently cease,  being  resumed  soon  after  light  again  has  access  to 
the  plant. 

(4)  If  glass  of  different  colors  be  interposed  in  the  path  of  the 
sun's  raj^s,  it  will  be  shortly  seen  that  orange  light  differs  from 
violet  light  in  its  effects  upon  the  rate  of  the  evolution  of  the 
bubbles. 

(5)  Place  around  the  base  of  the  test-tube  a  few  fragments  of 


306 


ASSIMILATION. 


ice,  in  order  to  appreciably  lower  the  temperature  of  the  water. 
At  a  certain  point  it  will  be  observed  that  no  bubbles  are  given 
off,  and  their  evolution  does  not  begin  again  until  the  water  be- 
comes warm. 

(6)  Examine,  at  the  close  of  the  series  of  simple  experiments, 
some  of  the  leaves  with  iodine  solution,  for  the  detection  of 
starch.  Even  with  no  precaution  the  chlorophyll  granules  will 
reveal  the  presence  of  a  considerable  amount  of  the  first  visible 
product  of  assimilation,  namely,  starch.  Lastly,  keep  a  second 
uninjured  spray  of  the  same  plant  in  the  light  for  a  time,  and 
then  in  darkness  for  a  day  or  two,  after  which  examine  it  for 
starch ;  probably  after  this  lapse  of  time  no  starch  can  be  de- 
tected, for  although  it  has  been  made  in  the  light,  in  darkness  it 
has  been  consumed  in  the  various  activities  of  the  plant. 

815.  According  to  the  accepted  theory,  light  consists  of  waves 
which  are  set  in  motion  in  a  tenuous  elastic  medium  termed  the 
ether.  The  existence  of  this  medium  is  made  known  to  us  only 
b\r  the  phenomena  which  light  itself  presents ;  but,  having  as- 
sumed its  existence,  the  phenomena  of  light  can  be  explained. 
The  tenuity  of  this  medium,  which  fills  all  space,  far  exceeds 
that  of  any  known  gas,  and  its  elasticit}'  is  far  higher  than  that 
of  anjr  known  elastic  solid.  In  it  a  luminous  body  sets  in  mo- 
tion undulations  which  produce  upon  the  retina  the  sensation  of 
light;  upon  differences  in  the  amplitude  and  the  duration1  of 
these  undulations  depend  differences  in  the  intensity  and  the 
color  of  the  light  which  reaches  the  eye.2 


1  The  terms  just  employed,  namely,  amplitude  and  duration,  seem  hardly 
applicable  to  waves  of  such  incredible  minuteness  and  velocity  as  those  named 
in  the  following  table  :  — 


Color  of 
light. 

Red     . 

Orange 

Yellow 

Green 

Blue   . 

Indigo 

Violet 


Number  of  waves  of  light  in  one 
second  of  time. 

,  477  millions  of  millions. 

,  506 

.  535 

,  577 


Length  of  each  wave. 

650  millionths  of  a  millimeter. 

609  ' 

576          « 

536 

498  ' 

470 

442 


2  "The  intensity  of  the  luminous  impression  must  depend  upon  the  force 
of  the  atomic  blows  which  are  transmitted  to  the  optic  nerves,  and  it  is  also 
evident  that  this  force  must  be  proportional  to  the  square  of  the  velocity  of 
the  oscillating  atoms,  or,  what  amounts  to  the  same  thing,  to  the  square  of  the 
amplitude  of  the  oscillation  ;  assuming,  of  course,  that  the  oscillations  are 
isochronous.  The  connection  of  color  with  the  time  of  oscillation  is  not  so 


TYPES    OF   ENERGY.  307 

816.  Light  and  assimilation  proper.     Energy  has  been  defined 
as  the  power  of  doing  work.     Of  this  there  are  two  types :  the 
energy  of  actual  motion  (sometimes  termed  kinetic),  and  the 
energy  of  position  (known  as  potential).     The  illustration  of 
their  difference  is  usually  given  as  follows :    A  ball  thrown  up- 
wards has  the  power  of  overcoming  the  force  of  gravity  tending 
to  pull  it  down,  and  possesses  energy  of  motion  ;  suppose  the 
ball  at  the  end  of  its  course  is  lodged  upon  some  projecting 
shelf,  then  its  energy  of  motion  disappears,  and   it  now  pos- 
sesses energy  of  position.     Whenever  it  is  dislodged,  it  will  fall 
with  the  same  power  which  was  required  for  its  ascent.     From 
this  and  similar  examples  it  is  plain  that  one  form  of  energy 
can  be   changed  into  another;  when  one  seems  to  disappear, 
it  has  in  fact  merely  been  converted  into  some  other. 

817.  These  t}rpes  of  energy  are  to  be  found  in  molecules  as 
well  as  in  masses  of  matter.     It  is  held  that  all  molecules  of  all 
matter  are  in  a  state  of  motion,  invisible,  but  none  the  less  real. 
One  form  of  such  invisible  kinetic  energy  is  heat,  and  another 
is  radiant  light,  where  the  energy  of  motion  is  embodied  in  the 
vibrations  or  undulations  of  the  ethereal  medium.     A  third  form 
is  that  of  electrical  separation ;    and  still  another,  with  which 
Physiology  deals  especially,  is  known  as  chemical  separation,  of 
which  a  familiar  illustration  may  be  given  :  An  atom  of  oxygen 
has  so  strong  an  attraction  for  one  of  carbon,  that  if  the  two 
are  united,  it  is  difficult  to  separate  them,  the  force  required 
to  do  this  being  comparable  to  that  demanded  to  raise  a  weight 
to  a  certain  height.     As  in  the  latter  case  the  weight  held  in 
its  raised  position  represents  by  that  position  the  force  which 
was   employed   to   raise  it,   so  the  separated   atoms  represent 
energy  of  position  ready  to  be  again  converted  into  energy  of 
motion.1 


obvious  ;  and  why  it  is  that  the  waves  of  ether  beating  with  greater  or  less  rapid- 
ity on  the  retina  should  produce  such  sensations  as  those  of  violet,  blue,  yellow, 
or  red,  the  physiologist  is  wholly  unable  to  explain.  We  have,  however,  an 
analogous  phenomenon  in  sound,  for  musical  notes  are  simply  the  effects  of 
waves  of  air  beating  in  a  similar  way  on  the  auditory  nerves  ;  and,  as  is  well 
known,  the  greater  the  frequency  of  the  beats,  or,  in  other  words,  the  more 
rapid  the  oscillations  of  the  aerial  molecules,  the  higher  is  the  pitch  of  the  note. 
Red  color  corresponds  to  low,  and  violet  to  high  notes  of  music,  and  the  gra- 
dations of  color  between  these  extremes,  passing  through  various  shades  of 
yellow,  green,  blue,  and  indigo,  correspond  to  the  well-known  gradations  of 
musical  pitch"  (Cooke:  Chemical  Philosophy,  1882,  p.  189). 

1  It  is  seldom  that  one  of  these  forms  of  molecular  energy  when  exhibited  in 
the  phenomena  of  living  beings  is  not  associated  with  some  other  form.     Thus 


308  ASSIMILATION. 

818.  The  conversion  of  the  energy  of  the  motion  of  the  ethe- 
real medium  (in  radiant  light)  into  chemical  separation  of  oxy- 
gen from  the  carbon  of  carbonic  acid,  and  the  production  of 
this  treasured  energy  under  other  forms,  is  the  chief  office  of  the 
plant. 

819.  Attention  has  already  been  called  (see  page  306)  to  the 
well-known  fact  that  a  beam  of  sunlight  is  composed  of  rays  or 
lines  of  undulations  differing  both  in  respect  to  their  amplitude 
and  velocity.    Hence  it  is  to  be  expected  that  in  their  action  on 
the  plant  these  rays,  which  are  in  fact  vehicles  of  kinetic  energy, 
must  have  diverse  effects. 

820.  Classification  of  the  rays  of  the  spectrum.     When  a  beam 
of  sunlight  is  transmitted  through  a  triangular  prism,  it  is  broken 
up  into  its  constituent  rays,  which,  falling  upon  a  screen,  form 
what  is  known  as  a  spectrum.      The  colors  of  the  spectrum 
grade  from   red   at  one   end,   through   orange,  yellow,   green, 
blue,  and  indigo,  to  violet.     The  violet  rays  are  bent  further 
from  their  course  by  the  prism  than  any  of  the  others  above 
spoken  of,  and  hence  are  termed  the  most  refrangible ;  experi- 
ment has  also  shown  that  these  highly  refrangible  rays  are  most 
efficient  in  producing  the  chemical  changes  long  known  to  be 
attributable  to  light:  for  this  reason  they  have  been  denomi- 
nated chemical  (or  sometimes  actinic)  rays.     The  red  rays  are 
bent  far  less  from  their  course  than  any  of  the  others  above  men- 
tioned, and  hence  they  are  termed  the  least  refrangible.     It  is 
at  the  red  end  of  the  visible  spectrum  that  the  greatest  amount 
of  heat  is  found.     The  rays  which  constitute  yellow  and  orange 
light  are  of  medium  refrangibility ;  they  are  the  most  distinctly 
luminous.     It  is  proper,  therefore,  for  convenience,  to  distin- 
guish rays  of  the  solar  spectrum  as  chemical,  luminous,   and 
heat  rays,  according  to  the  dominant  effect  which  they  produce. 
But  it  should  be  stated  that  each  of  these  three  groups  may 
share  some  of  the  work  specially  belonging  to  the  others ;   and 
further,  that  beyond   the  visible  spectrum  are  rays  which  are 
efficient  in  accomplishing  certain  kinds  of  work.     These  latter 
are  known   respectively   as  the  ultra-violet  and   the   ultra-red 
rays. 

Before  examining  the  action  of  these  different  rays  of  light 
upon  the  assimilative  activity  of  chlorophyll  granules,  inquiry 
must  be  made  as  to 

absorption,  which  is  essentially  a  process  of  molecular  adhesion,  is  accompanied, 
as  is  capillary  attraction,  by  electrical  disturbances.  In  no  case  is  energy  lost : 
one  form  disappears  only  to  reappear  in  some  other. 


PASSAGE   OF   LIGHT   THROUGH   LEAVES.  309 

821.  The  depth  to  which  light  can  penetrate  green  tissues.   This 
can  be  ascertained  approximately  by  a  simple  apparatus  sug- 
gested by  Sachs.1     A  pasteboard  tube,  a  foot  or  so  in  length 
and  about  an  inch  in  diameter,  is  cut  at  one  end  so  as  to  fit 
around  the  eye  very  closely  and  allow  no  rays  to  enter  except 
through  the  other  end  of  the  tube.     If  a  thin  leaf  be  placed 
over  the  distal  end  of  the  tube,  and  it  be  held  towards  a  bright 
light,  a  large  portion  of  the  light  will  be  received  by  the  eye. 
If  leaf  after  leaf  be  placed  over  the  first,  the  green  color  soon 
gives  way  to  a  dull  red,  and   finally   is  excluded   altogether. 
The  same  apparatus  shows  to  what  depth  light  can  penetrate 
superposed  layers  of  green  cells  taken  from  a  stem  or  from  thick 
leaves.2 

822.  The  quality  of  the  light  which  penetrates  a  leaf,  or  which 
has  passed  through  one  layer  of  cells  containing  chlorophyll,  is 
shown  b}r  means  of  the  spectroscope.      From  what  has  been 
shown  (p.  296) ,  it  is  clear  that  the  light  which  acts  on  the  cells 
below  the  first  layer  exposed  to  the  sun's  rays  must  be  different 
from  the  incident  rays  themselves.      The  light  which  reaches 
the  deeper  tissues  of  a  leaf  has  passed  through  more  than  one 
film  of  green  tissue. 

823.  The  degree  of  intensity  of  white  (that  is,  uncolored)  light 
most  favorable  to  assimilation  has  not  been  determined  with 
certainty.     The  lowest  limit  at  which  any  assimilation  has  been 
observed  is  considerably  above  that  at  which  etiolated  chloro- 
phyll turns  green.8 

824.  It  has  been  shown 4  that  very  intense  white  light,  even 
after  it  has  been  deprived  of  nearly  all  of  its  heat  rays,   can 
destroy  the  vitality  of  vegetable  cells.     Considerably  before  the 
death  of  the  cells  from  this  cause,  the  chlorophyll  granules  in 
them  lose  all  their  coloring-matter,   even  when  they  preserve 
their  general  form,  and  having  once  lost  their  green  color,  do 
not  afterwards  regain  it. 

1  Handbuch  der  Experimental-physiologie,  1865,  p.  5. 

2  But  it  has  been  shown  by  Haukel  that  the  angle  at  which  a  beam  of  light 
strikes  a  plate  of  glass  makes  a  noticeable  difference  in  the  amount  of  the  chemi- 
cal rays  which  can  pass  through  it ;  thus  while  at  a  vertical  angle  81  per  cent 
of  the  rays  are  transmitted,  the  rest  being  absorbed,  at  an  angle  of  60°  the 
amount  transmitted  is  reduced  to  71  per  cent,  and  at  80°  to  33  per  cent.     The 
subject  as  relating  to  plants  has  not  received  the  attention  it  deserves  (Berichte 
iiber  die  Verhandlungen  der  Sachsischen  Gesellschaft  der  Wissenschaften). 

3  Sachs  :  Experimental-physiologic,  1865,  p.  8. 

*  Pringsheim  :  Monatsberichte  der  Berlin  Akademie,  1879. 


310  ASSIMILATION. 

825.  Colored  light  and  assimilation.     Daubeny,  in  1835,  was 
the  first1  to  experiment  systematically  upon  this  subject.     His 
method 2  of  investigation  was  as  follows :    "A  certain  number 
of  fresh  leaves,  which  presented  in  each  case  an  extent  of  surface 
as  nearly  as  possible  equal,  and  had  been  previously  ascertained 
to  give  out  equal  quantities  of  oxygen,  were  introduced  severally 
into  jars  filled  with  water  impregnated  with  carbonic  acid  gas, 
placed  on  the  surface  of  a  pneumatic  trough,  and  exposed  for 
a  certain  time  to  the  influence  of  the  solar  rays.      The  jars  in 
which  the  leaves  thus  selected  stood,   were  severally  covered 
over  by  a  wooden  screen  which  intercepted  all  light  from  the  in- 
cluded jar,"  excepting  in  front,  where  a  frame  was  fitted,  into  which 
(1)  colored  glass  or  (2)  flat  bottles  filled  with  differently  colored 
liquids  could  be  fastened,  so  that  the  light  reaching  the  leaves 
could  be  variously  modified.     The  amount  and  character  of  the 
gas  escaping  into  the  upper  part  of  each  jar  were  carefully 
determined.     The  leaves  used  were  those  of  Brassica  oleracea, 
Salicorma,  Fucus,  Tussilago,  Cochlearia  Armoracia,  and  Mentha 
viridis.    Besides  plain  glass,  the  following  colored  varieties  were 
employed :   orange,   red,  blue,  purple,  green ;  while  the  liquids 
used  were,  for  blue,  ammonio-sulphate  of  copper,  and  for  red, 
port  wine. 

In  all  cases  Daubeny  determined  the  amount  of  gas  given  off 
by  the  leaves,  and  afterwards  analyzed  it  in  order  to  ascertain 
the  percentage  of  oxygen.  He  concluded  from  his  experi- 
ments,8 "  that  the  effect  of  light  upon  plants  corresponds  with 
its  illuminating  rather  than  with  its  chemical,  or  its  calorific 
influence." 

826.  J.  W.  Draper,  in  1844,  published  an  account  of  his  ex- 
periments upon  the  relations  of  green  plants  to  light,  as  regards 
the  amount  of  assimilative  activity  indicated  by  the  oxygen  given 

1  Senebier  and  others  had  already  conducted  some  inconclusive  experiments 
in  nearly  the  same  field. 

2  On  the  Action  of  Light  upon  Plants,  and  of  Plants  upon  the  Atmosphere 
(Philosophical  Transactions,  1836,  p.  149). 

The  activity  of  assimilation  proper,  as  will  be  seen  later,  can  be  measured 
with  a  very  close  approximation  to  accuracy,  by  the  amount  of  oxygen  gas 
which  is  set  free  from  the  assimilating  tissues,  or,  what  amounts  to  substan- 
tially the  same  thing,  by  the  amount  of  carbonic  acid  decomposed  by  them. 
For  the  sake  of  uniformity,  the  word  assimilation  is  to  be  used  in  the  follow- 
ing paragraphs,  even  where  the  authorities  cited  refer  to  the  process  under 
the  terms  decomposition  of  carbonic  acid,  evolution  of  oxygen,  etc.  The  term 
assimilation,  in  its  restricted  sense,  was  adopted  by  Sachs  (1863). 
8  Philosophical  Transactions,  1836,  p.  151. 


'S  EXPERIMENTS.  311 


off  during  exposure  to  different  rays  of  the  solar  spectrum  .  From 
his  results  it  appears  that  "the  rays  which  cause  the  decomposi- 
tion of  carbonic  acid  gas  have  the  same  place  in  the  spectrum  as 
the  orange,  the  yellow,  and  the  green  ;  the  extreme  red,  the  blue, 
the  indigo,  and  the  violet  exerting  no  perceptible  effect."  1 

Draper  lays  great  stress  upon  the  interesting  fact  previously 
noticed  by  Dauben}",  that  the  chemical  rays  appear  to  have  no 
effect  upon  the  work  of  assimilation.  He  does  not,  however, 
offer  any  explanation  of  the  curious  fact  that  the  chemical  activ- 
ity of  the  plant  is  dependent  upon  other  r&ys  than  the  chemical 
for  its  excitation. 

827.  The  principal  results  obtained  with  submerged  water 
plants  by  Cloez  and  Gratiolet,2  who  exposed  Potamogeton  and 

1  A  Treatise  on  the  Forces  which  produce  the  Organization  of  Plants,  1844, 
p.  177.     The  method  of  experimenting  is  detailed  by  Draper  as   follows  : 
"  Having,  by  long  boiling  and  subsequent  cooling,  obtained  water  free  from 
dissolved  air,  I  saturated  it  with  carbonic  acid  gas.     Some  grass  leaves,  the 
surfaces  of  which  were  carefully  freed  from  any  adherent  bubbles  or  films 
of  air  by  having  been  kept  beneath  carbonated  water  for  three  or  four  days, 
were  provided.      Seven  glass  tubes,  each  half  an  inch  in  diameter  and  six 
inches  long,  were  filled  with  carbonated  water,  and  into  the  upper  part  of  each 
the  same  number  of  blades  of  grass  were  placed,  care  being  taken  to  have  all 
as  near  as  could  be  alike.     The  tubes  were  inserted  side  by  side  in  a  small 
pneumatic  trough  of  porcelain.     It  is  to  be  particularly  remarked  that  the 
blades  were  of  a  pure  green  aspect,  as  seen  in  the  water  ;  no  glistening  air- 
film,  such  as  is  always  on  freshly  gathered  leaves,  nor  any  air  bubbles,  were 
attached  to  them.     Great  care  was  taken  to  secure  this  perfect  freedom  from 
air  at  the  outset  of  the  experiments. 

"The  little  trough  was  now  placed  in  such  a  position  that  a  solar  spectrum, 
kept  motionless  by  a  heliostat  and  dispersed  by  a  flint-glass  prism  in  a  hori- 
zontal direction,  fell  upon  the  tubes.  By  bringing  the  trough  nearer  to  the 
prism  or  moving  it  farther  off,  the  different  colored  spaces  could  be  made  to 
fall  at  pleasure  on  the  inverted  tubes.  The  beam  of  light  was  about  three 
fourths  of  an  inch  in  diameter.  In  a  few  minutes  after  the  commencement 
of  the  experiment  the  tubes  on  which  the  orange,  yellow,  and  green  light  fell 
commenced  giving  off  minute  gas  bubbles  ;  and  in  about  an  hour  and  a  half 
a  quantity  was  collected  sufficient  for  accurate  measurement. 

"The  gas  thus  collected  in  each  tube  having  been  transferred  to  another 
vessel  and  its  quantity  determined,  the  little  trough,  with  all  its  tubes,  was 
freely  exposed  to  the  sunshine.  All  the  tubes  now  commenced  actively  evolv- 
ing gas,  which,  when  collected  and  measured,  served  to  show  the  capacity  of 
each  tube  for  carrying  on  the  process.  If  the  leaves  in  one  were  more  sluggish, 
or  exposed  a  smaller  surface  than  the  others,  the  quantity  of  gas  evolved  in 
that  tube  was  correspondingly  less.  As  may  be  readily  supposed,  I  never 
could  get  tubes  so  arranged  as  to  act  precisely  alike  ;  but  after  a  little  practice 
I  brought  them  sufficiently  near  to  equality.  And  in  no  instance  was  this 
testing-process  of  the  power  of  each  tube  for  evolving  gas  omitted  after  the 
experiment  in  the  spectrum  was  over." 

2  Annales  de  Chimie  et  de  Physique,  ser.  3,  tome  xxxii.,  1851,  p.  67. 


312 


ASSIMILATION. 


Myriophyllum  to  the  action  of  light  colored  by  passing  through 
glass,  may  be  stated  as  follows :  The  activity  of  the  plant  in 
decomposing  carbonic  acid  diminishes  with  glasses  used  in  the 
order  given  :  (1)  uncolored  "  ground "  glass,  (2)  yellow,  (3)  un- 
colored  transparent  glass,  (4)  red,  (5)  green,  (6)  blue.  By  all 
the  experimenters  now  referred  to,  the  evolved  gas  was  collected 
and  examined. 

828.  Measurement  of  the  amount  of  assimilation.      Sachs,  in 
1864,  appears  to  have  been  the  first  to  employ  the  now  well- 
known  method  of  measuring  the   activity  of  the   assimilative 
process   by  counting   the   bubbles   of  gas  which  are  given  off 
by  a  submerged  water  plant  (see  814).     Since  the   gas  given 
off  by  the  plant  is  not  pure  oxygen,  but  is  variable  in  compo- 
sition,1 the  method  cannot  be  regarded   as   sufficiently  precise 
for  very  accurate  experiment ;    but  as  it  admits  of  such  rapid 
change  in  all  external  conditions,  it  answers  for  all  practical 
purposes. 

829.  The  effect  of  colored  light  upon  the  assimilative  activity 
of  plants  not  submerged,  as  in  the  above  experiments,  but  in 
the  air,  was  first  examined  by  Cailletet,2  in  1867.     He  placed 
the  plant  under  bell-jars  containing  air  with  eighteen,  twenty- 

1  For  remarks  upon  the  possible  errors  which  may  attend  the  use  of  this 
method,  consult  Miiller  (Pringsheim's  Jahrb.  vi.,  1868,  p.  478). 

2  L.  Cailletet  placed  leaves  in  jars  filled  with  air  containing  from  18  to  30 
per  cent  of  carbonic  acid,  and  then  exposed  these  to  light  which  had  passed 
through  colored  glass.     In  one  case  the  light  was  transmitted  through  a  solu- 
tion of  iodine  in  carbon  bisulphide.     After  an  exposure  of  from  eight  to  ten 
hours,  the  amount  of  carbonic  acid  remaining  undecomposed  by  the  action  of 
the  leaves  was  found  to  be  as  follows  :  — 


Per  cent  of  carbonic  acid 

Medium. 

in  the  air. 

.Remarks  as  to  chemical  activity 
of  light 

18  p.  c. 

21  p.  c. 

30  p.c. 

Iodine  In  CS2 

18 

21 

30 

Photographic  paper  not  blackened. 

Green  glass 

20 

30 

37 

Argentic  chloride  slowly  discolored. 

Violet  glass 

18 

19 

28 

Sensitive  paper  blackened  rapidly. 

Blue  glass 

17 

16.50 

27 

It                                       it                                      tt 

Bed  glass 

7 

5.50 

23 

No  blackening  of  argentic  chloride 

or  sensitized  paper. 

Yellow  glass 

5 

1 

18 

Paper  not  blackened. 

Ground  glass 

0 

0 

2        j  Paper  discolored  rapidly. 

Two  points  must  be  specially  noticed  :  (1)  the  striking  effect  of  the  large 
amount  of  carbonic  acid  in  the  third  series  ;  (2)  the  anomaly  presented  by  the 
green  glass,  which  is  quite  unexplained.  It  is  to  be  regretted  that  no  fuller 
account  of  the  character  of  the  glasses  used  is  given  (Comptes  Rendus,  Ixv., 
1867,  p.  322). 


TIMIRIAZEFF'S  RESEARCHES.  313 

one,  or  thirty  per  cent  of  carbonic  acid,  and  made  of  red,  yellow, 
green,  blue,  violet,  and  colorless  glass.  His  results  agree  in 
general  with  those  obtained  by  the  other  methods. 

830.  In  1870  further  investigations  in  the  same  subject  were 
made  by  Pfeffer.1     The  following  is  a  resume  of  the  results  of 
his  experiments  with  the  leaves  of  five  different  plants  exposed 
to  colored  light :    Only  the  visible  rays  of  the  spectrum  cause 
decomposition  of  carbonic  acid  ;  and  in  this  process  the  brightest, 
that  is,  the  yellow  rays,  are  as  efficient  as  all  the  others  taken  to- 
gether, while  the  most  refrangible  rays,  those  which  act  most  en- 
ergetically upon  chloride  of  silver,  have  only  very  slight  influence 
upon  the  work  of  assimilation. 

Every  color  of  the  spectrum  may  be  said  to  possess  a  specific 
quantitative  influence  upon  assimilation.  This  influence  remains 
unchanged  whether  the  color  is  isolated,  combined  with  one,  or 
with  all  the  other  colors  of  the  spectrum  when  it  acts  upon  a 
part  of  a  plant  containing  chlorophyll. 

831.  Examination  of  the  spectrum  of  chlorophyll  (779)  shows 
that  the  part  of  the  spectrum  which  absorbs  most  of  the  rays  is 
that  which  is  pre-eminently  its  chemical  end  ;  but  by  all  the  ob- 
servers whose  results  have  been  cited  in  the  text,  it  is  held  that 
the  chemical  end  is  that  which  is  least  efficient  in  assimilation. 
With  the  exception  of  the  narrow  though  strong  absorption-band 
in  the  red,  all  the  deep  absorption-bands  of  chlorophyll  and  its 
solutions  belong  at  the  violet  or  chemical  end  of  the  spectrum. 
Miiller  and  Timiriazeff,  cited  in  the  notes,  have  endeavored  to 
investigate  this  anomaly. 

832.  Timiriazeff,2  in  a  series  of  researches  in  1877,  experi- 
mented upon  the  slender  leaves  of  Bamboo,  which  he  placed 
in  tubes  of  small  calibre  containing  air  of  known  composition, 

1  Arbeiten  des  botan.  Inst.  in  Wurzburg,  1871,  p.  1. 
The  following  works  may  also  be  cited  :  — 

A.  von  Wolkoff,  Einige  Untersuchungen  iiber  die  Wirkung  des  Lichtes  von 
verschiedener  Intensitat  auf  die  Ausscheidung  der  Gase  durch  Wasserpflanzen. 
Pringsh.  Jahrb.,  v.,  1866,  p.  1. 

Adolf  Mayer,  Production  von  organischer  Pflanzen-Substanz  bei  Ausschluss 
der  chomischen  Lichtstrahlen,  Versuchs-Stationen,  ix. ,  ]  867,  p.  396. 

N.  J.  C.  Miiller,  Untersuchungen  iiber  die  Diffusion  der  atmospharischen 
Gase  in  der  Pflanze  und  die  Gasausscheidung  unter  verschiedenen  Beleucht- 
ungsbedingungen,  Pringsh.  Jahrb.,  vi.,  1867,  478  ;  and  vii.,  1869,  145. 

Timiriazeff,  Botanische  Zeitung,  1869,  p.  169. 
'  Prillieux,  Ann.  des  Sc.  nat.,  se"r.  5,  tome  x.,  1869,  p.  305. 

Baranetzky,  Botanische  Zeitung,  1871,  p.  193. 

2  Annales  de  Chimie  et  de  Physique,  ser.  5,  tome  xii.,  1877,  p.  355. 


814  ASSIMILATION. 

and  exposed  to  different  parts  of  a  large  spectrum  formed  by  a 
hollow  prism  filled  with  carbon  bisulphide.  By  employing  a  nar- 
rower slit  for  the  light  than  that  used  by  previous  experimenters, 
he  obtained  an  exposure  of  the  leaves  to  a  very  limited  portion 
of  the  spectrum  ;  and  to  this  difference  in  his  apparatus  he  chiefly 
attributes  his  results,  which  are  at  variance  with  those  of  his 
predecessors.  Assuming  that  the  results  of  his  analysis  of  the 
evolved  gas  are  accurate,  they  indicate  that  the  amount  of  car- 
bonic acid  decomposed  by  leaves  is  proportional  to  the  distri- 
bution of  effective  calorific  energy  in  the  spectrum. 

Timiriazeff l  in  his  earlier  paper  did  not  himself  attempt  to  apply 
his  results  to  an  explanation  of  the  peculiar  relations  of  the  rays 
of  the  spectrum  to  assimilation  ;  but  Van  Tieghem,  who  sub- 
stantially adopts  the  results  of  Timiriazeff,  gives  the  following 
application  of  them  to  the  associated  phenomena.  He  calls  atten- 
tion to  the  fact  that  the  maximum  of  decomposition  of  carbonic 
acid,  under  the  conditions  of  TimiriazefTs  experiments,  takes 
place  at  the  deep  absorption-band  of  chlorophyll,  between  B 
and  C ;  and  therefore  concludes  that  the  decomposition  of  car- 
bonic acid  by  leaves  exposed  to  solar  radiation  depends  on  two 
elements:  (1)  the  elective  absorption  of  the  chlorophyll,  and 
(2)  the  calorific  energy  of  the  absorbed  radiations.  According 
to  this  view,  the  most  efficient  radiations  must  be  those  which, 
being  best  absorbed  by  the  chlorophyll,  possess  at  the  same  time 
the  greatest  calorific  energy.  Hence,  (1)  the  extreme  red  and 
the  dark  heat- rays,  in  spite  of  their  extraordinary  calorific  energy, 
have  no  effect,  because  they  pass  through  chlorophyll  without 
visible  absorption  ;  and  (2)  the  blue  rays,  which  are  very  strongly 
absorbed,  exert  scarcely  any  effect,  owing  to  their  feeble  calorific 
energy.3 

833.  TimiriazefFs  results  should  be  compared  with  those  of 
Engelmann,  who  finds  that  for  green  cells  the  absolute  maximum 
of  assimilative  activity  lies  in  the  red,  between  the  lines  B  and  C, 
at  the  point  of  the  first  and  most  pronounced  absorption- band  of 
chlorophyll,  and  that  there  is  also  more  or  less  activity  in  the 
blue  at  F.  If  the  cells  are  not  of  a  green  color,  the  maximum  of 
activity  is  in  some  other  point ;  thus  in  the  case  of  bluish-green 
cells  it  is  in  the  yellow,  and  in  that  of  red  cells  in  the  green. 

Engelmann's  method  is  based  upon  the  extraordinary  sensi- 

1  Ann.  de  Chimie  et  de  Physique,  ser.  5,  toine  xii.,  1877,  p.  394,  and  Ann. 
des  Sc.  nat.,  ser.  7,  tome  ii.,  p.  99. 

2  Traite  de  Botanique,  1884,  p.  149. 


ENGELMANN'S  RESEARCHES.  315 

tiveness1  of  certain  bacteria  to  the  presence  of  free  oxygen.  By 
an  ingenious  device,  simple  in  its  application,  it  is  possible  to 
determine  the  parts  of  the  spectrum  in  which  an  assimilating  cell 
or  filament  gives  off  oxygen  most  copiously.  Under  the  stage 
of  the  microscope  is  placed  a  microspectroscope,  which  throws 
a  clear  spectrum  upon  any  object  on  the  glass  slide  in  its  place 
on  the  stage,  for  instance  a  filament  of  an  alga.  The  alga  is 
placed  upon  the  slide  in  water  which  contains  numbers  of  the 
common  Bacterium  (B.  Termo),  easily  procured  from  putrescent 
matters.  If  it  is  kept  from  the  light,  or  is  exposed  to  only  very 
faint  light,  all  assimilative  activity  is  suspended,  and  the  bacteria 
after  a  time  are  quiescent.  But  when  light  in  sufficient  amount 
is  permitted  to  pass  through  the  specimen,  assimilative  activity  is 
at  once  manifested,  and  the  evolution  of  oxygen  from  the  filament 
brings  the  bacteria  into  rapid  movement.  If,  instead  of  white 
light,  the  rays  from  the  spectroscope  are  passed  through  the 
specimen,  the  activity  of  the  bacteria  is  equally  manifest,  but  it 
is  confined  to  a  comparatively  small  part  of  the  spectrum  ;  the 
bacteria  collecting  chiefly  at  the  points  which  are  known  to  coin- 
cide with  the  absorption-bands  of  chlorophyll.2  When  a  some- 
what thick  cell  is  employed,  there  is  a  noticeable  difference 
between  the  amount  of  activity  on  its  upper  and  under  side. 
The  figures  show  the  ratio  of  activity  of  assimilation  between 
the  under  side  first  exposed,  and  the  upper  side  which  receives 
light  that  has  first  passed  through  a  green  film. 

B-C.  D.  DJE.  E-b.  F.  FJQ. 

Lower    ....     100.  48.5  37.  24.  36.5          10. 

Upper     ....       36.5  94.  100.  52.  22.  12. 

It  is  to  be  noted  that  Engelmann  did  not  in  any  case  find  any 
assimilation  in  uncolored  chlorophyll,  even  when  the  light  was 
tempered  by  the  interposition  of  a  colored  medium  (compare  850).8 
He  has  proved  that  assimilation  proper  takes  place  only  in 

1  According  to  Engelmann,  the  sensitiveness  of  bacteria  is  so  great  that  by 
their  reaction  the  trillionth  part  of  a  milligram  of  oxygen  can  be  detected 
(Botanische  Zeitung,  1883,  p.  4).     Clerk  Maxwell's  estimate  of  the  weight  of 
a  molecule  of  oxygen  was  one  thirteen  trillionth  of  a  milligram  (Philosophical 
Magazine,  1873,  p.  453). 

2  It  is  interesting  to  compare  these  determinations  of  the  point  of  greatest 
assimilative  efficiency  in  the  spectrum  with  the  results  of  Langley's  researches 
upon  the  distribution  of  energy  in  the  spectrum  (American  Journal  of  Science, 
xxv.,  1883,  p.  169). 

8  Botanische  Zeitung,  1882,  p.  419 ;  1883,  p.  17. 


316  ASSIMILATION. 

protoplasm  which  contains  coloring-mater,  as  for  instance  the 
chloroph}'!!  granules,  the  colored  granules  in  algae,  etc. 

834.  Artificial  light  and  assimilation.     De  Candolle l  exposed 
the  submerged  leaves  of  several  species  of  plants  to  the  light 
emitted  b}r  six  Argand  lamps,  and  failed  to  obtain  thereby  any 
evolution  of  gas.     He  estimated  that  the  lamps  had  about  five 
sixths  of  the   intensity   of  sunlight.      In   this  experiment  the 
light,  though  insufficient  to  cause  the  evolution  of  gas,  restored 
etiolated  plants  to  their  original  green  color. 

835.  When,  however,  a  submerged  water  plant  is  exposed  to 
the  rays  from  a  calcium  light 2  (as  that  of  an  ordinary  projecting 
lantern),  there  is  a  copious  evolution  of  gas  from  its  leaves.    The 
light  from  burning  magnesium  wire  is  also  sufficient  to  cause  the 
decomposition  of  carbonic  acid  and  the  evolution  of  oxj-gen.8 

836.  The  influence  of  the  electric  light  upon  assimilation  has 
been  investigated  by  numerous  observers.    Dehe'rain,   who  ex- 
perimented in  the  Palais  de  PIndustrie,  in  Paris,  found  that  the 
total  assimilation  produced  in  the  leaves  of  Anacharis  Canaden- 
sis,  during  an  exposure  for  five  daj's,  was  not  equal  to  that  which 
followed  exposure  to  sunlight  for  a  single  hour.4     Siemens  has 
shown  that  (1)  many  plants  do  not  require  any  period  of  rest 
during  the  day,  but  thrive  under  continued  illumination  by  elec- 
tric light  and  sun-light ;    (2)  electric  light,  properly  regulated, 
accelerates  growth,  and  produces  upon  plants  effects  comparable 
to  those  produced  by  sun-light.6 

837.  Temperature  and  assimilation  proper.     In  certain  cases 
the  minimum  temperature  at  which  assimilation  can  take  place  is 
only  slightly  above  the  freezing-point  of  water.     Boussingault 6 
found  that  the  leaves  of  the  larch  decompose  carbonic  acid  at 
a  temperature  of  from  0°.5-2°.5  C. ;  while  Kraus7  gives  the 

1  Mem.  pres.  par  divers  Savans,  a  1'Institut  des  Sciences,  tome  i.,  1806, 
p.  333,  and  Physiologic  vegetale,  1832,  p.  131. 

Biot,  in  1840  (Froriep's  Notizen,  xiii.  10),  when  measuring,  in  Spain,  the 
length  of  a  degree  of  latitude,  found  that  the  light  from  the  powerful  signal- 
ling apparatus  used  was  not  sufficient  to  cause  any  evolution  of  gas  from  sub- 
merged plants  of  Agave  Americana. 

2  Prillieux  :  Comptes  Rendus,  Ixix.,  1869,  p.  408. 

8  Heinrich  :  Versuchs-Stationen,  xiii.,  1871,  p.  153. 

*  Annales  Agronomiques,  tome  vii.,  1881,  p.  385. 

8  Proceedings  of  the  Royal  Society,  xxx.,  pp.  210,  295,  and  Report  of  the 
British  Association  for  the  Advancement  of  Science,  1881,  p.  474. 

6  Ann.  des  Sc.  nat.,  ser.  5,  tome  x.,  1868,  p.  336. 

1  Kraus  (Pringsh.  Jahrb.,  vii.,  p.  522)  placed  seedlings  of  Lepidium  sativum 
in  the  dim  light  of  the  back  of  a  room,  where  after  six  days  the  cotyledons 


ASSIMILATION  AND  TEMPERATURE. 


317 


minimum  temperature  for  assimilation  by  Anacharis,  Lepidium, 
and  Betula  as  3°-5°  C. ;  and  Heinrich1  gives  it  as  2°.5-4°.5  C. 
for  Hottonia. 

The  'maximum  temperature  at  which  assimilation  can  occur 
in  Anacharis  2  is  between  45°  and  50°  C. ;  in  Hottonia,8  just  be- 
low 56°  C. 

The  optimum*  temperature  for  Hottonia  appears  to  be  not 
far  from  31°  C. 


showed  no  trace  of  starch.  The  plants  were  then  distributed  in  three  rooms 
of  the  temperatures  mentioned  in  the  annexed  table,  and  with  the  results  there 
detailed  :  — 


After 

12°.8-13°.7  C. 

6°.  9-6°.5  C. 

0°.3-0°.6  C. 

2  hours. 

The  first  starch  granules  appear 

No  starch. 

No  starch 

in  the  chlorophyll  cells  on  the 

margin  of  the  leaves. 

3  hours. 

Starch  in  the  whole  tip,  margins, 

Some  traces  of  starch  at 

" 

and  petiole. 

margins  of  the  leaves. 

5  hours. 

Starch  in  the  whole  upper  half  of 

Tip  and  narrow  edge  with 

« 

the  leaf. 

starch. 

13  hours. 

The  whole  leaf  contained  starch. 

Margin  with  much,  sur- 

« 

face  with  little  starch. 

1  Versuchs-Stationen,  xiii.,  1871,  p.  136. 

2  Schutzenberger  and  Quinquaud  :  Comptes  Rendus,  Ixxvii.,  1873,  p.  272. 
8  Heinrich :  Versuchs-Stationen,  xiii.,  1871,  p.  136. 

*  Heinrich's  figures  are  so  instructive  that  they  are  here  presented  in  the 
following  table,  which  gives  the  number  of  bubbles  of  gas  passing  off  from  the 
cut  surface  of  single  leaves  of  Hottonia  during  the  space  of  five  minutes  :  — 
Temp.C.°  No.  of  bubbles. 

11  145-160 

12 180-190 

13 215- 

15 245-255 

17 255-265 

21 325-360 

22 375- 

25 390-450 

81  547-580 

37 420-517 

43 225-255 

50 110-220 

56 0 

The  student  must  be  reminded  that  the  amount  of  gas  which  comes  off 
in  this  experiment  with  submerged  plants  is  not  an  exact  measure  of  the 
assimilation. 


318  ASSIMILATION. 

838.  The  amount  of  carbonic  acid  unfavorable  to  assimilation. 

Experiments  made  by  Saussure 1  at  the  beginning  of  this  cen- 
tury proved  beyond  question  that  plants  are  not  tolerant  of  an 
atmosphere  containing  a  large  proportion  of  carbonic  acid.  In 
carbonic  acid  alone,  or  even  in  an  atmosphere  containing  66 
per  cent  of  this  gas,  vegetation  was  speedily  destroyed.  It  was 
shown,  however,  that  if  the  plants  were  exposed  to  full  light, 
the3T  could  sustain  8  per  cent  of  carbonic  acid  without  injury. 
Saussure  thought  that  the  presence  of  free  oxygen  is  necessary 
to  the  assimilative  work  of  the  leaf. 

839.  In  1849,  Daubeny 2  carried  on  an  extensive  series  of  re- 
searches, chiefly  upon  plants  allied  to  the  dominant  vegetation 
of  the  Carboniferous  period,  namely,  ferns  and  their  allies,  from 
which  it  appeared  that  even  for  these  plants  an  amount  of  car- 
bonic acid  above  10  per  cent  is  injurious.     Five  species  were 
placed  in  a  receptacle  containing  about  46  liters  of  air,  and  to 
this  air  was  added  one  per  cent  of  carbonic  acid,  and  also  one 
per  cent  daily  thereafter,  until  the  amount  present  reached  20 
per  cent.      This  proportion  was  kept  for  twenty  days,  small 
amounts  being  added,  as  occasion  required,  to  make  up  for  loss 
by  leakage.     On  the  thirteenth  day  a  sensible  impairment  of 
the   plants  was  noticed ;  and  at  the  end  of  thirty  days  all  of 
them  had  been  more  or  less  damaged,  most  having  lost  their 
fronds. 

840.  Boussingault,8  in   1864,   conducted  a  series  of  experi- 
ments in  order  to  ascertain  whether  the  presence  of  free  oxygen 
in  an  atmosphere  containing  carbonic  acid  is  necessary  to  the 
work  of  assimilation.     The  results  of  his  researches  are  given 
as  follows :  — 

(1)  Leaves  exposed  to  sunlight,  in  pure  carbonic  acid,  do  not 
decompose  this  gas,  or  if  at  all,  very  slowly. 

(2)  Leaves  exposed  to  sunlight  in  an  atmosphere  containing 
a  mixture  of  common  air  and   carbonic  acid   decompose  the 
latter  gas  rapidly ;  but  the  oxygen  of  the  air  has  no  part  in  this 
operation,  since, 

(3)  Leaves  exposed  to  sunlight  rapidly  decompose  carbonic 
acid  gas  when  this  gas  is  mixed  with  nitrogen,  hydrogen,  car- 
bonic oxide,  or  carburetted  hydrogen. 

1  Saussure:  Recherches  chimiques  sur  la  vegetation  (Paris,  1804),  p.  29. 
An  earlier  experiment  was  made  by  Percival. 

2  Report  of  British  Association,  1849,  p.  56  ;  and  1850,  p.  159. 
8  Agronomic,  iv.,  1868,  p.  301. 


RELATIONS   OF   CARBONIC   ACID   TO   ASSIMILATION.     319 

841.  The  amount  of  carbonic  acid  most  favorable  to  assimilation. 

The  results  of  the  most  exhaustive  study  of  the  amount  of  car- 
bonic acid  most  favorable  to  assimilation  have  been  given  by 
their  recorder  as  follows  :  — 

(1)  Increase  in  the  amount  of  carbonic  acid  in  the  air,  up  to 
a  certain  limit  (the  optimum),  favors  the  evolution  of  oxygen 
by  plants  ;  beyond  this  it  is  more  or  less  injurious. 

(2)  The  optimum  of  carbonic  acid  is  different  for  different 
plants :  for  Glyceria  spectabilis  on  clear  days  it  is  between  8 
and  10  per  cent ;  for  Typha  latifolia,  between  5  and  7  per  cent ; 
for  Oleander,  somewhat  less. 

(3)  Any  given  increase  in  the  amount  of  carbonic  acid  below 
the  optimum  favors  the  evolution  of  oxj'gen  far  more  than  a 
similar  increase  above  the  optimum  hinders  it. 

(4)  The  stronger  the  intensity  of  the  light  the  more  the  evolu- 
tion of  oxygen  is  favored  by  increase  in  the  amount  of  carbonic 
acid  up  to  the  optimum  ;    and  when  this  limit  is  passed  the 
evolution  is  checked  so  much  the  less. 

(5)  From  (4)  it  follows  that  the  influence  of  the  intensity  of 
the  light  on  the  evolution  of  oxygen  is  greater  in  proportion  to 
the  amount  of  carbonic  acid  in  the  air. 

842.  Ratio  of  the  oxygen  evolved  by  plants  to  the  carbonic  acid 
decomposed.     The  volume  of  oxygen  evolved  by  plants  during 
assimilation  proper   is  very  nearly  that  of  the  carbonic  acid 
decomposed.1 

Numerous  experiments  by  Boussingault  exhibit  this  relation 
in  a  very  striking  manner.  In  forty-one  experiments  the  volume 
of  carbonic  acid  was  to  that  of  the  oxygen  set  free  as  100  :  98.7. 

1  Saussure  (Recherches  chimiques  sur  la  vegetation,  1804,  pp.  40,  59)  is 
regarded  as  the  first  to  indicate  this.  He  arrived  at  this  conclusion  by  experi- 
menting upon  a  number  of  plants  under  different  conditions.  His  first  recorded 
experiment  consisted  in  surrounding  seven  plants  of  Vinca  (Periwinkle)  with 
an  atmosphere  containing  a  known  quantity  of  carbonic  acid  gas.  The  plants 
were  exposed  to  sunlight  from  five  to  eleven  o'clock  in  the  morning  for  six 
days,  after  which  the  air  in  the  bell-jar  was  examined. 

Air  in  the  jar  Air  in  the  jar 

before  the  experiment.  after  the  experiment. 

Nitrogen 4199  cubic  cent.  .     .     4338  cubic  cent. 

Oxygen      .     .          .     .     1116          "  •     •     1408 

Carbonic  acid      .     .     .       431          "  0          " 


Total  volume       .     .     .     5746          "  .     .     5746          " 

Saussure's  conclusion  is  that  plants,  in  decomposing  carbonic  acid,  assimi- 
late a  part  of  the  oxygen  gas  therein  contained,  and,  further,  that  the  amount 
of  carbon  retained  by  the  plant  bears  a  definite  relation  to  the  amount  of  C02 
taken  up  by  it, 


320 


ASSIMILATION. 


The  following  table  by  Boussingault J  is  very  instructive,  as  it 
shows  the  relation  of  volume  between  the  amount  of  carbonic 
acid  consumed  and  the  oxygen  evolved  in  assimilation ;  and 
also  the  decomposing  power  of  various  kinds  of  plants  under 
different  conditions.2 


Plants. 

CO,  disap- 
pearing. 

Oxygen 
appear- 
ing. 

Time  of 
exposure 
to  light. 

Surface 
of 
leaves. 

CO,  decomposed 
per  square  deci- 
meter each  hour. 

Constitu- 
tion of  at- 
mosphere. 

c.  c. 

c.  c. 

h.  m. 

cm.  sq. 

c.  c. 

Cherry  laurel 

5.2 

5.9 

4   0 

134 

.8 

CO, 

<« 

23.2 

22.9 

4   0 

124 

4.7 

CO,  -(-air. 

«< 

4. 

4.5 

4   0 

90 

1.0 

CO, 

" 

19.6 

19.9 

4   0 

90 

5.5 

CO,  +  air. 

Pine 

13.0 

13.0 

7   0 

204 

.9 

CO, 

" 

18.1 

17.8 

7   0 

204 

1.3 

CO2  +  air. 

Oak 

4.9 

4.0 

4   0 

224 

.5 

CO, 

" 

26. 

24.7 

4   0 

224 

2.8 

CO,  -fair. 

Holly 

5.1 

4.9 

5   30 

52 

1.8 

«« 

Mistletoe 

9.9 

9.9 

5   0 

100 

2. 

" 

843.  The  gas  emitted  during  the  process  of  assimilation  proper 
is  not  pure  ox3'gen.     Both  Daubenj' 8  and  Draper 4  found  varia- 
ble amounts  of  nitrogen  in  all  the  cases  examined  by  them. 

844.  What  are  the  products  of  assimilation  proper?     It  has 
now  been  shown  under  what  conditions  the  green  tissues  of  a 
plant  decompose  carbonic  acid  and  evolve  oxj-gen.6      As  the 
chief  result  of  this  decomposition  and  its  associated  processes, 
there  is  formed  within  the  cells  which  contain  chlorophyll  a  carbo- 
hydrate of  some  kind.      This  carbohydrate  contains  the  same 
elements  as  the  carbonic  acid  and  the  water  from  which  it  was 
produced,  but  it  contains  less  oxygen  than  the  total  amount 
found  in  those  substances  taken  together.     Hence  the  process 
of  assimilation  is  essentially  one  of  reduction.     There  is,  how- 
ever, no  substantial  agreement  as  to  the  nature  or  constitution 
of  the  primary  carbohydrate  formed  by  it. 

The  difficulty  which  attends  the  investigation  of  assimilation 

1  Agronomic,  iv.,  1868,  p.  286. 

2  A  well-known  relation  of  volume  between  oxygen  and  carbonic  acid  may 
here  be  pointed  out  ;  namely,  that  "free  oxygen  occupies  the  same  bulk  as  the 
carbonic  acid  produced  by  uniting  it  with  carbon." 

8  Philosophical  Transactions,  1836. 

"  In  every  instance  which  I  have  examined,  the  gas  evolved  from  leaves 
is  not  pure  oxygen,  but  a  variable  mixture  of  oxygen  and  nitrogen.  This  result 
is  of  uniform  occurrence"  (Chemistry  of  Plants,  1844,  p.  182). 

6  For  an  account  of  the  transient  evolution  of  oxygen  under  exceptional 
circumstances  where  carbonic  acid  is  not  present,  see  Miiller's  Handbuch  der 
Botanik,  1880. 


THE   FIKST  VISIBLE  PRODUCT.  321 

is  apparent  at  a  glance.  The  raw  materials,  the  apparatus, 
and  the  ultimate  products  of  manufacture  are  known ;  but  the 
intermediate  processes  by  which  chlorophyll  granules  under  the 
influence  of  certain  rays  of  light  can  cause  the  dissociation  of 
carbon  from  the  oxygen  with  which  it  is  combined  in  carbonic 
acid,  and  bring  about  the  synthesis  of  an  organic  substance  from 
materials  wholly  inorganic,  are  not  at  present  known. 

845.  The  wide  field  which  the  synthesis  of  organic  from  inor- 
ganic matter  opens  to  conjecture  has  not  been  left  unoccupied. 
It  is  generally  admitted  that  in  assimilation  there  is  first  formed 
some  ternary  substance,  namely,  one  which  contains  the  three 
elements,  carbon,    hydrogen,    and   oxygen ;    and   further,   that 
this  contains  less  oxygen  than  the  two  inorganic  matters,  car- 
bonic acid   and   water,  from  which   it   is   produced,  taken   to- 
gether.     Exactly  what  the  ternary  substance  is,   or  how  the 
dissociation  or  reduction  is  carried  on  in  the  chlorophyll  granule, 
is  still  left  in  doubt. 

846.  Starch  (C6H10O5)  is  the  first  visible  product  of  assimila- 
tion, as  was  first  pointed  out  by  Sachs  in  1862. a     Although 
Sachs  appears  to  have  held  at  one  time  that  it  is  the  first  pro- 
duct, his  later  expressions  are  more  guarded,  and  simply  state 
the  fact  universally  admitted,  namelj",  that  starch  is  the  first 
product  which  the  microscope  can  detect.     When  a  seedling  has 
been  kept  for  a  time  in  a  dimly  lighted  room,  its  cotyledons  and 
other  leaves  grow  pale  or  etiolated,  and  if  they  are  examined 
for  starch,  no  trace  of  it  will  be  found.     But  upon  a  very  short 
exposure  of  the  plant  to  the  direct  rays  of  the  sun,  provided  the 
other  conditions  are  favorable,  a  certain  amount  of  starch  will 
appear  in  the  chlorophyll  granules  of  the  cells  at  the  margin  of 
the  leaves.     If  the  plant  is  again  withdrawn  from  the  light,  its 
scanty  store  of  starch  is  speedily  consumed,  but  on  renewed  in- 
solation the  loss  is  made  good ;  this  process  can  be  repeated 
many  times.     From  the  constant  appearance  of  starch  in  the 
chlorophyll  granules  under  the  above  circumstances  it  has  been 
generally  recognized  as  the  first  visible  product  of  assimilation 
proper.     But  it  has  obviously  such  a  complex  molecular  struc- 
ture that  chemists  are  unwilling  to  believe  that  its  formation  in 
the  plant  is  not  preceded  by  the  production  of  some  simpler 
substance.      Furthermore,  there  are  a  few  cases  in  which  oil 
replaces  starch  as  the  first  visible  product,  thus  indicating  that 
there  may  be  some  earlier  product  possibly  common  to  both. 

1  Botanische  Zeitung,  1862  ;  Flora,  1862. 
21 


322  ASSIMILATION. 

847.  Glucose.     It  is  held  by  some  that  this  product  is  glucose 
(C,.H12OG)   or  some  substance  having  the  same  atomic  propor- 
tions of  these  elements.      Early  and  not  well-defined  views  in 
regard  to  glucose  may  be  replaced  by  the  following  statement  of 
a  theory  widely  taught. 

848.  Formic    aldehyde    hypothesis.      According   to   Gautier,1 
chlorophyll  exists  in  two  conditions,  white  chlorophyll,  rich  in 
hydrogen,  and  green  chlorophyll,  poorer  in  this  element.     By  his 
hypothesis  the  yellow  ray  absorbed  by  the  assimilating  tissues 
furnishes  a  certain  amount  of  energy  which  is  partially  con- 
verted into  heat,  and  promotes  evaporation  of  water  (transpira- 
tion) ;  and  at  the  same  time  it  permits  the  chlorophyll  granule  to 
decompose  the  water  with  which  the  protoplasmic  mass  is  satu- 
rated.    In  the  presence  of  CO2  and  H2O  the  reducing  process 
gives  rise  to  formic  acid  (CH^O^,  which  in  its  turn  is  reduced  to 
formic  (or  methylic)  aldehyde,  CH2O.     The  latter  has  the  same 
atomic  proportions  as  glucose  (C6H12Oti). 

849.  Whether,  in  assimilation,  the  ternary  substance  be  for- 
mic aldehyde,  or  glucose,  or  starch,  it  is  certain!}-  a  substance 
capable  of  undergoing  further  oxidation,  and  hence,  chemically 
speaking,   an    unsaturated   compound.     When  this  unsaturated 
compound  is  oxidized,2  a  definite  amount  of  energy  of  motion 
is  set  free,  and  this  is  manifested  to  us  under  one  of  its  man}- 
phases,  namelv :  (1)  movements  of  the  whole  plant,  as  in  some 
of  the  lowest  organisms ;  (2)  movements  of  liquids  within  the 
plant,  as  in  the  transfer  of  matter  to  points  of  consumption ; 
(3)  heat ;    (4)  electrical  disturbances,  and  all  the  proper  vital 
activities  correlated  with  these.     The  energy  of  motion  in  solar 
radiance  is  treasured  for  a  time  in  the  ternaiy  and  derivative 
products,  thence  to  be  released  as  occasion  requires. 

850.  It  is  proper  to  refer  at  this  point  to  a  novel  view  in 
regard  to  the  product  of  assimilation  which  has  received  much 
adverse  criticism  ;  namely,  that  of  Pringsheim.8     Attention  has 
already  been  called  to  the  interesting  observations  by  this  bota- 
nist on  the  constitution  of  chlorophyll  granules.     In  prosecuting 
his  investigations  he  became  convinced  that  the  peculiar  colored 
substance  which  is  extruded  from  the  granules  under  the  influ- 
ence of  certain  agents  is  a  product  of  assimilation.      To  this 
product  he  gave  the  name  hypochlorin.    According  to  him,  when 


1  La  Chimie  des  Plantes.     Revue  Scientifique,  Feb.  10,  1877,  p.  767. 
3  Compare  Claude  Bernard,  Lemons  sur  les  Phenomenes  de  la  Vie,  1878. 
8  Jahrb.,  xii.,  1879-1881,  p.  288. 


EARLY   HISTORY.  323 

anj'  active  cells  containing  chlorophyll  granules  are  subjected 
to  conditions  favorable  to  assimilation,  hypochlorin  is  formed 
in  considerable  amount ;  but  when  the  conditions  for  assimi- 
lation are  not  present,  only  traces  of  it  are  produced.  Prings- 
heira  used  an  entirely  novel  method  of  experimenting ;  namely, 
that  of  subjecting  the  chlorophyll  granules  to  the  action  of 
intense  light  from  which  the  heat  rays  had  been  extracted  as 
perfectly  as  possible ;  and  under  these  conditions  he  failed  to 
detect  an}-  hypochlorin,  but  observed  a  marked  increase  in  the 
amount  of  CO2  given  off  as  in  ordinary  respiration  (see  Chapter 
XI.).  Hence  he  arrived  at  the  conclusion  that  assimilation 
proper  is  the  characteristic  office  of  chlorophyll  granules  solely 
on  account  of  their  pigment,  which  tempers  the  light  reaching 
them.  According  to  him,  the  pigment,  by  its  absorption  of  the 
so-called  chemical  rays,  serves  as  a  regulatory  screen  gov- 
erning the  amount  of  light,  and  so  controlling  the  amount  of 
respiration  and  assimilation  proper. 

851.  Outline  of  the  early  history  of  assimilation.     The  follow- 
ing extracts  from  the  works  of  early  experimenters  upon  the 
relations  of  green  leaves  to  the  atmosphere  show  the  manner  in 
which  the  problem  of  assimilation  was  first  attacked. 

852.  Priestle}'1  discovered  in  17712  that  air  in  which  candles 
can  no  longer  burn,  and  which  is  irrespirable,  can  be  restored  to 
its  original  condition  by  the  presence  in  it,  for  a  time,  of  vig- 
orous plants.     The  account  below  is  given  in  his  own  words  : 

"  Finding  that  candles  would  burn  very  well  in  air  in  which  plants 
had  grown  a  long  time,  and  having  had  some  reason  to  think,  that 
there  was  something  attending  vegetation  which  restored  air  that  had 
been  injured  by  respiration,  I  thought  it  was  possible  that  the  same 


1  Experiments   and  Observations  on  Different  Kinds  of  Air  (3d  edition, 
1781),  p.  51. 

2  In  1754  Bonnet  published  his  observations  upon  the  behavior  of  leaves 
in  water.     It  is  well  known  that  when  green  leaves  are  immersed  in  water  and 
exposed  to  sunlight  for  a  time,  bubbles  of  air  appear  on  their  surface.     Bonnet 
believed  that  the  leaves  drew  common  air  from  the  water  and  this  swelled  into 
conspicuous  bubbles  under  the  heat  of  the  sun.     He  was  confirmed  in  this 
belief  upon  ascertaining  that  bubbles  did  not  appear  on  green  leaves  ex- 
posed in  water  which  has  been  boiled  to  expel  the  air  (Recherches  sur  1'usage 
des  Feuilles  dans  les  Plantes,  p.  26).     If  we  consider  the  state  of  chemical 
science  at  the  time  of  Bonnet's  researches,  his  error  is  in  no  wise  surprising. 
It  is  now  known  that  the  bubbles  which  Bonnet  took  to  be  air  are  nearly 
pure  oxygen  which  escapes  as  a  by-product  of  assimilation.     But  from  water 
which  has  been  boiled,  all  the  carbonic  acid  essential  to  assimilation  has  been 
expelled. 


324  ASSIMILATION. 

process  might  also  restore  the  air  that  had  been  injured  by  the  burning 
of  candles. 

"  Accordingly  on  the  17th  of  August,  1771, 1  put  a  sprig  of  mint  into 
a  quantity  of  air,  in  which  a  wax  candle  had  burned  out,  and  found 
that,  on  the  27th  of  the  same  month,  another  candle  burned  perfectly 
well  in  it.  This  experiment  I  repeated,  without  the  least  variation  in 
the  event,  not  less  than  eight  or  ten  times  in  the  remainder  of  the 
summer.1 

"  Several  times  I  divided  the  quantity  of  air  in  which  the  candle 
had  burned  out,  into  two  parts,  and  putting  the  plant  into  one  of  them, 
left  the  other  in  the  same  exposure,  contained  also  in  a  glass  vessel 
immersed  in  water,  but  without  any  plant;  and  never  failed  to  find 
that  a  candle  would  burn  in  the  former,  but  not  in  the  latter.  I  gen- 
erally found  that  five  or  six  days  were  sufficient  to  restore  this  air,  when 
the  plant  was  in  its  vigour;  whereas  I  have  kept  this  kind  of  air  in  glass 
vessels  immersed  in  water  many  months  without  being  able  to  perceive 
that  the  least  alteration  had  been  made  in  it." 

853.  Ingenhonsz  in  1779  showed  that  light  is  necessary  to 
assimilation.  He  proved  experimentally  that  the  purification 
of  air  does  not  go  on  in  darkness,  but  that  light  is  essential. 
His  statements  are  here  given  :  — 

"  Plants  not  only  have  a  faculty  to  correct  bad  air  in  six  or  ten  days, 
by  growing  in  it,  as  the  experiments  of  Dr.  Priestley  indicate,  but  they 
perform  this  important  office  in  a  complete  manner  in  a  few  hours. 
This  wonderful  operation  is  by  no  means  owing  to  the  vegetation  of 
the  plant,  but  to  the  influence  of  the  light  of  the  sun  upon  the  plant. 
.  .  .  This  operation  of  plants  diminishes  towards  the  close  of  the  day, 
and  ceases  entirely  at  sunset,  except  in  a  few  plants  which  continue 
this  duty  somewhat  longer  than  others.  This  office  is  not  performed 
by  the  whole  plant,  but  only  by  the  leaves  and  the  green  stalks  that 
support  them.  Acrid,  ill-scented,  and  even  the  most  poisonous  plants 
perform  this  office  in  common  with  the  mildest  and  the  most  salutary."  2 

1  Priestley  thought  that  this  effect  upon  the  air  is  due  to  the  growth  of  the 
plant,  an  idea  which  will  be  shown  in  Chapter  XII.  to  be  wholly  erroneous.    On 
pages  50  and  52  of  the  volume  quoted  above  are  the  following  statements : 
"One  might  have  imagined  that  since  common  air  is  necessary  to  vegetable,  as 
well  as  to  animal  life,  both  plants  and  animals  had  affected  it  in  the  same  man- 
ner ;  and  I  own  I  had  that  expectation  when  I  first  put  a  sprig  of  mint  into  a 
glass  jar  standing  inverted  in  a  vessel  of  water  :  but  when  it  had  continued 
growing  there  for  some  months  I  found  that  the  air  would  neither  extinguish  a 
candle  nor  was  it  at  all  inconvenient  to  a  mouse  which  I  put  into  it.  ...  This 
restoration  of  the  air,  I  found,  depended  upon  the  vegetating  state  of  the  plant  ; 
for  though  I  kept  a  great  number  of  the  fresh  leaves  of  mint  in  a  small  quan- 
tity of  air  in  which  candles  had  burned  out,  and  changed  them  frequently,  for 
a  long  space  of  time,  I  could  perceive  no  melioration  in  the  state  of  the  air." 

2  Experiments  upon  Vegetables,  discovering  their  great  Power  of  purifying 
the  Common  Air  in  the  Sun-shine,  1779,  p.  xxxiii. 


APPROPRIATION   OF   NITROGEN.  325 

854.  Senebier 1  first  demonstrated  that  plants  obtain  all  their 
carbon  from  carbonic  acid  gas. 

855.  That  definite  quantitative  relations  exist  between  the 
amounts  of  carbonic  acid  decomposed,  carbon  retained,  and  oxy- 
gen evolved  by  the  plant,  was  first  pointed  out  by  Sanssure.2 


APPROPRIATION    OF   NITROGEN. 

856.  It  has  been  shown  that  all  land  and  many  water  plants 
contain  a  variable  amount  of  air  in  their  tissues,  chiefly  in  the 
intercellular  spaces  and  older  modified  cells  (trache'ids,  tracheae, 
etc.).     When  there  is  an  active  interchange  of  gases  by  any 
plant,  a  portion  of  the  nitrogen  contained  in  its  included  air  is 
very  likely  to  be  eliminated.     A  trace  of  nitrogen  is  so  generally 
found  with  the  oxygen  evolved  during  assimilation  proper,  that 
this   has   been   regarded  by  some  as  a  constant  accompaniment 
of  the  assimilative  process. 

857.  A  mount   of  nitrogen  in  the  plant.     Besides  the  free  nitro- 
gen which  constitutes  a  part  of  the  included  air  of  the  plant, 
there  is  a  certain  amount  of  combined  nitrogen  always  present 
in  active  cells  as  an  essential  component  of  their  living  matter. 
The  protoplasmic  matters  in  plants  contain  about  15  per  cent  of 
nitrogen  in  combination.     For  all  practical  purposes  they  may 
be  regarded  as  having  chemically  a  common  albuminous 8  basis 
(roughly  comparable  to  the  white  of  egg),  with  which  (as  has 

1  Memoires  Physico-chymiques,  1782. 

Many  of  Senebier's  observations  are  almost  identical  with  those  of  Ingen- 
housz  (as  given  in  his  "Nutrition  of  Plants"),  and  it  has  been  thought  by 
some  that  the  priority  of  the  above  discovery  belongs  rightfully  to  the  latter. 
It  is  to  be  remembered  that  at  the  date  at  which  both  of  these  experimenters 
were  working,  chemists  were  just  beginning  to  acquire,  through  the  studies 
of  Lavoisier,  clear  notions  in  regard  to  the  important  part  which  oxygen 
plays,  and  that  in  the  early  part  of  this  transition  period  an  obscure  nomen- 
clature renders  it  difficult  to  apportion  to  each  of  these  observers  his  proper 
share  of  credit. 

2  Recherches  chimiques  sur  la  vegetation,  1804. 

Some  of  the  relations  of  light  to  the  process  of  decomposition  of  carbonic 
acid  by  green  parts  of  plants  were  first  indicated  by  Daubeny,  and  further  ex- 
amined by  Draper.  The  subsequent  history  of  assimilation,  to  which  Sachs, 
Pfeffer,  Engelmann,  and  many  others  have  contributed,  has  been  referred  to 
in  the  text  and  in  citations  in  the  notes. 

8  Attention  may  again  be  called  to  the  various  expressions  employed  to 
designate  the  compounds  in  the  plant  which  resemble  albumin,  and  which 
have  been  collectively  termed  albuminoids.  Authors  have  made  a  distinction 


326  ASSIMILATION. 

been  seen  on  page  197)  there  is  always  intermingled  an  incon- 
stant amount  of  carbohydrates,  or  proper  food-materials,  etc. 
At  different  stages  in  the  life  of  a  cell  its  protoplasmic  matters 
may  pass  through  considerable  changes  of  form  and  structure, 
as  indicated  in  an  examination  of  a  ripening  seed  ;  but  under  all 
these  varying  conditions  nitrogen  in  combination  is  never  absent 
from  the  living  substance  of  the  plant. 

858.  For  the  formation  of  new  protoplasmic  matters  in  the 
plant,  supplies  of  nitrogen  in  an  available  form  must  be  fur- 
nished ;  for  healthful  growth,  these  supplies  must  be  adequate 
in  amount. 

859.  Dissolved  albuminous  matters  of  various  kinds  are  met 
with  in  the  sap  of  some  cells.     This  in  many  cases  appears  to 
be,  as  will  be  shown  later,  a  form  in  which  their  transport  from 
one  part  of  the  plant  to  another  is  secured.    A  small  number  of 
these  albuminous  substances  have  been  shown  to  be  ferments, 
which  play  a  very  important  part  in  the  nutrition  of  the  plant. 

860.  Although  by  far  the  greater  part  of  the  combined  nitro- 
gen of  the  plant  exists  in  one  or  more  of  the  combinations  men- 
tioned in  Chapter  XL,  there  is  often  to  be  detected  a  small  and 
variable  amount  as  a  nitrate l  (generally  potassic) ,  and  even  as 
a  salt  of  ammonia. 


between  certain  groups  of  these  bodies  as  they  are  represented  in  the  animal 
kingdom,  dividing  them  into  (1)  albuminous  matters  and  (2)  their  derivatives 
or  albuminoids  (see  Gorup-Besanez,  Lehrbuch  der  Chemie,  iii.,  1874,  p.  115). 
Although  the  latter  term,  without  the  restriction  here  noted,  is  in  common 
use  in  vegetable  physiology  to  designate  these  bodies,  an  objection  can  justly 
be  urged  against  its  employment,  on  account  of  the  more  common  use  in 
botany  of  the  word  albumen  with  an  entirely  different  signification  (see  Volume 
I.  p.  14). 

In  1838  Mulder  published  the  theory  that  all  these  bodies  are  practically 
derivatives  from  one  substance,  termed  by  him  proteine  (from  irpuTtvti),  to  be 
first)  ;  but  it  was  soon  shown  that  this  theory  was  erroneous,  and  it  has  been 
generally  abandoned.  The  term  introduced  by  Mulder  to  designate  the  hypo- 
thetical compound  common  to  all  these  bodies  has,  however,  been  since  em- 
ployed to  conveniently  denote  the  whole  class.  In  using  the  convenient  term 
protein  bodies,  or  proteids,  to  designate  the  members  of  this  group,  it  must  not 
be  understood  that  the  abandoned  theory  of  Mulder  is  taken  into  account  at  all. 

1  For  the  detection  of  nitrates  the  following  test  may  be  employed :  To  a 
drop  of  the  sap  under  examination  add  a  drop  of  a  solution  of  brucine,  mix, 
and  then  add  a  few  drops  of  concentrated  sulphuric  acid,  when,  if  a  nitrate  is 
present,  a  red  color  will  appear.  Sprengel's  reaction  may  also  be  used  :  One 
part  of  phenol  is  dissolved  in  four  parts  of  concentrated  sulphuric  acid,  and  two 
parts  of  water  are  added.  If  a  drop  of  this  solution  is  added  to  a  solid  nitrate, 
a  reddish  color  is  produced.  On  adding  strong  ammonia,  the  color  turns  green 
and  afterwards  yellow. 


SOURCES  OF  NITROGEN  FOR  THE  PLANT.      327 

861.  There  can  be  found  in  a  large  number  of  plants  a  small 
amount  of  certain  matters  termed  alkaloids,  which  contain  a  defi- 
nite percentage  of  nitrogen.     Such  are  morphia  in  the  poppy, 
quinia  in  Peruvian  bark,  caffeine  in  coffee,  etc.  (see  961). 

862.  In  most  analyses  the  combined  nitrogen  of  the  plant  is 
usually  rendered  as   "albuminoid."    The  percentages  in  a  few 
cases  are  here  given  : 1  — 

Red  clover,  full  blossom 3.7 

Sugar  beets 8  to  1.0 

Carrot  root 1.5 

Carrot  leaves 3.2 

Cabbage 1.5 

Winter  wheat 13.0 

Beans  (field) 25.5 

Apples 22  to  .52 

Of  these  amounts  about  16  per  cent  may  be  roughly  estimated 
as  the  content  of  nitrogen.  Therefore  in  such  a  case  as  the 
carrot  root  above  mentioned,  the  total  amount  of  nitrogen  is 
really  very  small  (0.24  per  cent)  ;  but  the  presence  of  this  small 
percentage  is  absolutely  essential  to  the  life  as  well  as  to  the 
health  of  the  plant. 

863.  Reserving  for  a  later  chapter  all  consideration  of  the 
numerous  chemical  transformations  which  nitrogenous  matters 
may  undergo  in  the  plant,  it  is  necessary  to  ask  now,  (1)  whence 
can  the  plant  obtain  adequate  supplies  of  available  nitrogen,  and 
(2)  how  can  the  plant  appropriate,  or,  to  use  an  equivalent  term, 
assimilate  them. 

864.  Sources  of  nitrogen  for  the  plant.     It  must  first  be  shown 
whence  nitrogen  is  not  supplied.     The  free  nitrogen  of  the  at- 
mosphere does  not  appear  to  be  directly  available  for  plants. 
Although  most  of  the  higher  plants  possess  an  aerating  system 
(see  p.  300),  through  which  atmospheric  air  can  easily  enter  and 
traverse  the  plant  and  be  brought  into  contact  with  the  tissues, 
the  nitrogen  which  forms  so  large  a  part  of  the  atmosphere  is 
not  utilized.     This  is  the  interpretation  of  experiments  in  cul- 
ture in  which  every  kind  of  combined  nitrogen  is  carefully  ex- 
cluded from  the  plants  while  they  have,  at  the  same  time  the 
free  nitrogen  of  the  atmosphere  in  an  unlimited  supply. 

865.  The  earliest2  systematic  investigations  relative  to  the 

1  For  other  cases  the  student  should  consult  the  tables  in  the  Appendix  to 
Johnson's  "How  Crops  Grow,"  ]868,  pp.  385-392. 

2  The  following  citations  refer  to  earlier  observations,  none  of  which,  how- 
ever, can  be  considered  as  having  fixed  any  important  points  relative  to  the  use 
of  atmospheric  nitrogen  by  plants  :  — 


328  ASSIMILATION. 

above  subject  were  made  by  Boussingault  in  1837, 1  who  era- 
ployed  the  following  method  :  In  calcined  soil,  supplied  with  dis- 
tilled water,  and  having  free  access  of  air,  clover  was  cultivated 
for  two  and  for  three  months,  and  at  the  end  of  that  time  it  was 
found  that  there  was  a  very  slight  gain  in  nitrogen  over  the 
amount  which  had  been  present  in  the  seed  sown.  In  two 
parallel  experiments  with  wheat  no  gain  was  observed.  One 
year  later,  peas,  clover,  and  oats  were  experimented  on ;  both 
the  peas  and  clover  gained  a  little  nitrogen,  but  there  was  no 
gain  whatever  in  the  case  of  the  oats.  Boussingault's  conclu- 
sions from  this  series  have  been  stated  as  follows  :  Under  several 
conditions  certain  plants  seemed  adapted  to  take  up  the  nitrogen 
in  the  atmosphere,  but  it  is  still  a  question  under  what  circum- 
stances and  in  what  state  the  nitrogen  is  fixed  in  the  plants. 

866.  It  was  not,  however,  until  1851  that  the  subject  received 
any  further  attention  from  Boussingault.     In  that  and  the  two 
subsequent  years  his  experiments  were  conducted  with  certain 
precautions,  by  which  the  plants  were  confined  in  limited  vol- 
umes of  air ;  and  in  no  case  was  an  unequivocal  gain  in  nitrogen 
to  be  detected.     In  1854  he  placed  plants  in  a  suitable  recep- 
tacle where  they  could  be  supplied  with  a  current  of  air  washed 
to  free  it  from  all  traces  of  combined  nitrogen.    The  atmosphere 
within  the  receptacle  was   furnished  with   from    two    to   three 
per  cent  of  carbonic  acid.     In  all  of  the  experiments,  part  of 
which  were  upon  leguminous  plants,  there  was  a  slight  loss  of 
nitrogen. 

867.  During  the  progress  of  the  experiments  now  alluded  to 
others  were  conducted  in  the  following  manner :    Plants  were 
placed  in  a  case  from  which  nearly  all  dust  could  be  excluded, 
but  which  would  allow  of  a  free  circulation  of  the  external  air ; 
and  under  these  circumstances  there  was  the  very  slight  gain  in 
nitrogen  equal  to  about  one  twelfth  of  that  contained  iu  the  seed 
sown.     Boussingault  attributed  this  almost  inappreciable  gain 

Priestley  :  Experiments  and  Observations  on  Different  Kinds  of  Airs,  iii., 
1772. 

Sanssure  :  Recherches  chimiques  sur  la  vegetation,  1804,  p.  205.  In  this 
will  be  found  a  short  account  of  the  results  of  the  previous  observers  and  also 
of  Saussure's  own  conclusions,  which  are,  —  that  plants  do  not  appropriate  any 
appreciable  amount  of  nitrogen  furnished  to  them  as  it  exists  in  the  atmosphere 
in  the  free  state. 

1  For  a  short  but  excellent  abstract  in  English  of  Boussingault's  researches, 
referred  to  in  the  text,  the  student  may  consult  Philosophical  Transactions  of 
the  Royal  Society  for  1861,  p.  447.  The  original  communications  are  in 
Annales  de  Chimie  et  de  Physique,  ser.  2,  tomes  Ixvii.  and  Ixix.,  1838. 


VILLE'S  EXPERIMENTS.  329 

to  the  ammonia  in  the  atmosphere,  and  also  to  organic  matters 
in  small  amount  which  may  have  entered  the  case  in  the  form  of 
very  fine  dust ;  but,  taking  into  consideration  all  the  conditions 
of  the  experiment,  he  was  not  inclined  to  the  belief  that  any 
nitrogen  had  been  received  by  the  plants  from  the  free  nitrogen 
of  the  atmosphere. 

868.  In  1855  and  1858  the  same  chemist  experimented  upon 
certain  plants  which  were  supplied  with  a  known  amount  of  com- 
bined nitrogen  in  some  available  form.     The  results  of  his  ex- 
periments have  been  formulated  as  follows :  (1)  There  was  no 
appropriation  of  free  nitrogen ;    (2)  There  was  a  slight  loss  of 
the  nitrogen  which  bad  been  supplied  to  the  plant;    (3)  The 
amount  of  assimilation  of  carbon  bore  a  close  relation  to  the 
amount  of  nitrogen  taken  up  by  the  plant. 

869.  From  1849  to  1854  Georges  Ville,  of  Paris,  conducted 
experiments  which  were  interpreted  as  showing  that  plants  can 
take  from  the  nitrogen  of  the  atmosphere  a  certain  part  of  that 
which  the}r  require.     In  the  autumn  of  1854  he  carried  on  a 
series  of  researches  at  the  Jardin  des  Plantes,  under  the  super- 
vision of  a  committee  appointed  by  the  French  Academy.     To- 
wards the  close  of  the  work  an  element  of  error  crept  into  it 
which  could  not  then  be  eliminated ;    but  as  to   the   result  of 
the  investigation  the  committee   reported,1  —  that   the   experi- 
ment made  at  the  Museum   d'Histoire   Naturelle   by  M.  Ville 
is  consistent  with  the  conclusions  which  he   has   drawn   from 
his  previous  labors. 

870.  In  1861  Lawes,  Gilbert,  and  Pugh,2  of  England,  pub- 


1  The  report  by  Chevreul  will  be  found  in  Comptes  Kendus,  xli.  p.  757. 
Results  so  directly  in  conflict  as  those  of  the  two  experi  men ters  referred  to  in 
the  text  led  others  to  investigate  this  subject,  and  in  1857-1859  an  exhaustive 
series  of  investigations  was  carried  on  at  Rothamsted,  England,  by  Lawes, 
Gilbert,  and  Pugh. 

Mene,  in  1851,  concluded  from  his  experiments  that  plants  do  not  appro- 
priate the  free  nitrogen  of  the  air. 

Roy  interpreted  the  results  of  his  own  experiments  as  showing  that  free 
nitrogen  dissolved  in  water  can  be  taken  up  by  plants. 

Luca  (1856)  suggested  that  the  air  surrounding  plants  maybe  ozonized,  and 
thus  the  nitrogen  in  it  converted  into  nitric  acid  and  made  available  for  the 
plants. 

Harting  (1855)  concluded  that  the  free  nitrogen  of  the  air  is  not  proved  to 
serve  directly  for  the  nutrition  of  the  plant. 

2  Philosophical  Transactions,  1861,  p.  431.     For  an  excellent  description 
and  drawing  of  the  complicated  apparatus  employed  in  this  capital  investiga- 
tion the  student  may  consult  Johnson's  "How  Crops  Feed,"  p.  30. 


330  ASSIMILATION. 

lished  the  results  of  a  series  of  experiments  upon  the  subject  of 
the  appropriation  of  nitrogen  by  plants.  These  experiments  were 
designed  to  settle  the  disputed  question.  Ever}"  conceivable  pre- 
caution was  taken  to  avoid  any  error,  and  the  plants  were  grown 
under  conditions  as  little  unlike  their  ordinary  surroundings  as 
possible.  Under  these  conditions  to  insure  healthy  growth,  they 
were  deprived  of  all  access  to  nitrogen  except  as  it  existed  in 
the  free  state  in  the  atmosphere  or  dissolved  in  the  water  sup- 
plied to  them.  It  was  found  that  no  plants  appeared  to  make 
use  of  the  free  nitrogen  of  the  atmosphere  or  of  the  nitrogen 
dissolved  in  water  supplied  to  their  roots.  But  in  certain  cases, 
especially  of  leguminous  plants  cultivated  in  the  open  air,  there 
is  an  apparent  gain  in  the  amount  of  nitrogenous  products  in 
the  plant  over  and  above  that  which  is  directly  attributable  to 
the  combined  nitrogen  furnished  to  it.1 

1  The  following  extracts  from  the  paper  by  Lawes,  Gilbert,  and  Pugh  will 
convey  a  clear  idea  of  the  cautious  manner  in  which  their  important  results 
are  reported  :  — 

"  The  results  obtained  with  Graminacese  in  1858  .  .  .  point  without  excep- 
tion to  the  fact  that  under  the  circumstances  of  growth  to  which  the  plants  were 
subjected,  no  assimilation  of  free  nitrogen  has  taken  place.  The  regular  pro- 
cess of  cell-formation  has  gone  on  ;  carbonic  acid  has  been  decomposed,  and 
carbon  and  the  elements  of  water  have  been  transformed  into  cellulose  ;  the 
plants  have  drawn  the  nitrogenous  compounds  from  the  older  cells  to  perform 
the  mysterious  office  of  the  formation  of  new  cells  ;  those  parts  have  been  de- 
veloped which  required  the  smallest  amount  of  nitrogen,  and  all  the  stages  of 
growth  have  been  passed  through  to  the  formation  of  glumes,  pales,  and  awns 
for  the  seed.  In  fact,  the  plants  have  performed  all  the  functions  that  it  is 
possible  for  a  plant  to  perform  when  deprived  of  a  sufficient  supply  of  com- 
bined nitrogen.  They  have  gone  on  thus  increasing  their  organic  constituents 
with  one  constant  amount  of  combined  nitrogen  until  the  percentage  of  that 
element  in  the  vegetable  matter  is  far  below  the  ordinary  amount  of  it,  —  that 
is,  until  the  composition  indicates  that  further  development  had  ceased  for 
want  of  a  supply  of  available  nitrogen.  Throughout  all  these  phases,  water 
saturated  with  free  nitrogen  has  been  passing  through  the  plant ;  nitrogen  dis- 
solved in  the  fluid  of  the  cells  has  constantly  been  in  the  most  intimate  contact 
with  the  contents  of  the  cells  and  with  the  cell-walls  "  (p.  523). 

Of  leguminous  plants  the  investigators  say,  "  In  those  cases  in  which  we 
have  succeeded  in  getting  leguminous  plants  to  grow  pretty  healthily  for  a 
considerable  length  of  time,  the  results,  so  far  as  they  go,  confirm  those  ob- 
tained with  Graminaceae,  not  showing  in  their  case,  any  more  than  with  the 
latter,  an  assimilation  of  free  nitrogen  "  (p.  526). 

Further,  they  say,  "  From  the  results  of  various  investigations,  as  well  as 
from  other  considerations,  we  think  it  may  be  concluded  that  under  the  cir- 
cumstances of  our  experiments,  on  the  question  of  the  assimilation  of  free 
nitrogen  by  plants,  there  would  not  be  any  supply  to  them  of  an  unaccounted 
quantity  of  combined  nitrogen  due  either  to  the  formation  of  oxygen  com- 


NITROGEN    COMPOUNDS   IN   RAIN  WATER.  331 

871.  Nitrogen  compounds  in  the  atmosphere.     The  atmosphere 
contains  minute  amounts l  of  combined  nitrogen  in  the  form  of 
ammonia,  nitric  acid,  and  nitrous  acid.     The  ammonia  is  be- 
lieved to  exist  (except  where  from  local  causes  there  is  an  escape 
of  free  ammonia  from  some  source)  combined  with  either  carbonic 
or  nitric  acid. 

872.  Nitrogen  in  rain-water.      The  nitrogen  compounds  are 
more  or  less  perfectly  removable  from  the  air  by  rain,  and  in 
solution  can  be  made  available  to  plants  through  the  soil.     It 
is  now  necessary  to  examine  the  results  of  analyses  of  rain- 
water in  order  to  ascertain  the  amount  of  nitrogen  contained 
in  it. 

The  following  data  are  taken  from  the  careful  experiments 
at  Rothamsted,  under  the  direction  of  Lawes,  Gilbert,  and  War- 
ington.  The  nitrogen  existing  as  nitric  acid  and  ammonia  in 
the  rainfall  of  one  year  is  not  far  from  3.3  pounds  per  acre.  The 
proportion  of  this  calculated  as  ammonia  is  between  2.3  and  2.6 
pounds  per  acre,  the  residue  being  given  as  nitric  acid.  Be- 
sides the  foregoing  substances,  there  is  also  a  small  amount  of 
nitrogenous  organic  matter  in  the  air  which  appears  in  the 
analyses  of  rain-water,  and  amounts,  according  to  Frankland,  to 
.19  parts  per  million  parts  of  water.  Taking  a  somewhat  lower 
estimate  than  this,  Lawes,  Gilbert,  and  Warington  give  the 
quantity  of  nitrogen  in  the  form  of  organic  matter  annually 


pounds  of  it  under  the  influence  of  ozone,  or  to  that  of  ammonia  under  the 
influence  of  nascent  hydrogen  "  (p.  540). 

But,  as  shown  by  Lawes,  Gilbert,  and  Pugh,  as  well  as  by  many  other  ex- 
perimenters,  leguminous  crops  appropriate  from  some  source  considerably  more 
nitrogen  than  do  grasses ;  for  instance,  under  apparently  similar  circumstances 
of  supply  of  combined  nitrogen. 

For  an  excellent  treatment  of  the  whole  matter  of  appropriation  of  nitrogen, 
the  student  should  consult  memoirs  by  Atwater,  "  On  the  Acquisition  of  Atmos- 
pheric Nitrogen  by  Plants"  (American  Chem.  Journ.,  vol.  vi.,  1885,  no.  6). 

1  The  following  figures  serve  simply  to  indicate  the  wide  range  in  results 
obtained  by  different  observers  who  have  investigated  the  amount  of  ammonia 
in  the  atmosphere.  The  data  are  from  Proceedings  of  Am.  Assoc.  for  Ad- 
vancement of  Science,  1857,  p.  152. 

Observer  Station  Amount  of  ammonia  in  one  million 

cubic  meters  atmosphere. 

Fresenius  .  Wiesbaden  (during  the  day)        ....  127.27  gr. 

"  •             "          (at  night) 219.47   " 

Kemp     .  .     Ireland 4423.00  " 

Ville      .  .     Paris 27.39   " 

Horsford  .     Boston  (in  July) 640.70  " 


332  ASSIMILATION. 

contributed  in  the  rain  as  1.08  pounds  per  acre.  "  We  may 
probably  take  4.5  pounds  per  acre  as  the  best  estimate  we  can 
at  present  give  of  the  total  combined  nitrogen  annually  supplied 
in  the  Rothamsted  rainfall.  This  is  only  about  two  thirds  as 
much  as  the  earlier  results  indicated  as  due  to  ammonia  and 
nitric  acid  alone.  ...  In  addition  to  the  combined  nitrogen 
carried  down  from  the  atmosphere  in  rain,  we  have  to  consider 
any  gain  to  the  soil  or  to  the  crop  by  direct  absorption  of  am- 
monia or  nitric  acid  from  the  air.  As  far  as  an}-  gain  from  the 
atmosphere  to  the  plant  itself  is  concerned,  there  is  very  little 
direct  experimental  evidence  on  the  point,  but  such  as  is  avail- 
able would  lead  to  the  conclusion  that  its  amount  is  practically 
immaterial.  As  to  the  amount  of  gain  by  absorption  by  the 
soil,  there  is  unfortunately  no  direct  or  satisfactory  evidence 
at  command.  From  such  evidence  as  does  exist,  we  are 
disposed  to  conclude  that  with  some  soils  the  amount  will 
probably  be  greater  and  with  others  less  than  that  supplied  by 
the  rainfall."  l 

873.  Direct  absorption  of  ammonia  by  leaves.      Under  certain 
circumstances  ammonia  can  be  absorbed  directly  by  leaves.    This 
will  be  further  adverted  to  under  "Appropriation  of  Organic 
Matters." 

874.  How  the  nitrogen  compounds  of  the  atmosphere  are  formed. 
It  is  a  familiar  fact  that  under  certain  circumstances  the  free  nitro- 
gen of  the  atmosphere  can  be  made  to  unite  with  oxygen  for  the 
production  of  nitric  acid ;  for  instance,  by  the  passage  of  a  spark 
of  electricity  through  a  confined  atmosphere  a  small  amount  of 
combined  nitric  acid  may  be  formed.     The  bearing  of  this  fact 
upon  the  existence  of  nitrogen  compounds  in  the  atmosphere  is 
very  obvious.     Schloesing,2  in  an  interesting  study  of  the  nitro- 
gen compounds  of  the  air  and  soil,  attributes  to  the  atmosphere 
a  very  important  office  in  forming  and  distributing  nitrogen  com- 
pounds.    According  to  him,  the  nitric  acid  contained  in  rain- 
waters on  escaping  from  the  soil,  where  it  is  only  lightly  held, 
finds  its  way  to  the  sea,  where  under  various  agencies  (notably 
that  of  vegetable  organisms  of  the  lowest  grade)  it  becomes, 
sooner  or  later,  changed  into  ammonia.     This  readily  escapes 
into  the  air,  and  is  carried  in  the  atmospheric  currents  to  all 
parts  of  the  world,  becoming  thereby  available  to  land  plants. 


1  Journal  Royal  Agricultural  Society,  vol.  xix.,  part  2,  1883. 

2  Comptes  Rendus,  tome  Ixxxi.,  1875.    The  same  idea  has  been  more  or  less 
treated  by  others. 


AVAILABLE   NITROGEN   IN  THE   SOIL. 


333 


875.  Available  nitrogen  in  the  soil.    When  animal  matters  rich 
in  nitrogen  undergo  rapid  putrefaction,1  they  give  rise  to  numer- 
ous compounds,  prominent  among  which  are  those  of  ammonia. 
Under  certain  conditions,  notably  the  presence  (1)  of  free  oxy- 
gen in  large  amount,  or  (2)  of  an  alkali,  or  an  alkaline  carbonate, 
such  animal  matters  are  also  slowly  broken  up,  and  nitrates  are 
formed.     The  process  by  which  various  compounds  of  nitrogen 
are  converted  into  nitrates  is  termed  nitrification.2 

876.  Vegetable  matters  which  contain  nitrogenous  substance 
in  the  usual  amount  may  likewise  undergo  decomposition ;  but 
owing  to  the  presence  in  such  matters  of  a  large  proportion  of 
carbohydrates,  for  instance  the  cellulose  of  the  cell-walls,  the 
process  of  decomposition  is  more  complex  than  in  animal  matters 
and  its  products  more  diverse.    Some  of  the  products  are  proba- 
bly identical  with  those  formed  from  the  decomposition  of  albu- 
minous matters  of  animal  origin  ;  namely,  ammonia,8  or  ammonia 
compounds,  and  nitrates;  but  the  larger  number  of  them  are 
compounds  which  are  nearly  or  quite  insoluble  and  have  been 
thought  to  be  inert.4     But  experiments  have  shown  that  under 
certain  conditions  these  less  available  compounds  of  nitrogen 


1  For  a  discussion  of  the  various  phases  and  conditions  of  decomposition  the 
student  is  referred  to  the  third  volume  of  this  series,  in  which  the  different 
forms  of  fermentation  and  putrefaction  are  to  be  treated.     It  is  enough  now  to 
note  that  these  processes  are  essentially  due  to  the  presence  and  activity  of 
minute  organisms,  —  the  lowest  fungi. 

2  The  student  will  find  in  Johnson's  "How  Crops  Feed,"  p.  289,  an  ex- 
cellent account  of  this  most  important  topic.     He  is  referred  also  to  Boussin- 
gault's  "Agronomic,"  1860,  and  various  articles  in  Versuchs-Stationen. 

3  The  following  data  indicate  the  amounts  of  nitrogen  in  certain  soils,  as 
determined  by  Boussingault  (Agronomic,  ii.,  1861,  pp.  14,  18).      The  reduc- 
tions to  pounds  per  acre  are  from  Johnson's  "  How  Crops  Feed,"  p.  276. 


Ammonia. 

Nitrogen  in  organic 

Source  of  the  SoU. 

per  cent. 

Ibs.  per  acre. 

per  cent. 

Ibs.  per  acre. 

Liebfrauenberg  (light  garden  soil) 

0.0020 

100 

.259 

12,970 

Bechelbronn  (wheat-field  clay) 

0.0009 

45 

.139 

6,985 

Argentan  (rich  pasture) 

0.0060 

300 

.513 

25,650 

Rio  Cupari,  S.  A.  (rich  leaf-mould) 

0.0525 

2,875 

.685 

34,250 

4  Experiments  by  Boussingault  (Agronomic,  i.  1860)  can  hardly  be  in- 
terpreted in  any  other  way.  One  reason  for  his  results  has  been  sought  in  the 
fact  that  he  employed  only  very  small  amounts  of  vegetable  matter  in  his  ad- 
mixtures of  soil ;  but  all  of  his  experiments  are  regarded  as  models  of  accuracy 


334 


ASSIMILATION. 


in  the  soil  can  be  turned  to  a  very  important  account  by  the 
plant. 

877.  Nitrogen  used  by  wild  and  cultivated  plants.     From  the 
sources   described,    wild    plants   obtain   a   sufficient  supply  of 
available  nitrogen.     In  some  localities,  notably  in  portions  of 
the  tropics  and  along  the   rich  alluvial  deposits  of  rivers,  the 
stores  of  available  nitrogen  are  so  abundant  that  all  vegetation 
flourishes  with  great  vigor,  and  even  cultivated  plants,  which  ap- 
pear to  be  more  exacting  than  wild  plants  in  their  demands  for 
nitrogen,  can  obtain  an  adequate  supply.     Further,  it  has  been 
abundantly  shown  by  the  long-continued  experiments  at  Rotham- 
sted,  that  the  same  soil,  unenriched  by  additions  of  manures,  can 
yield  even  after  twenty-five  years  enough  nitrogen  for  the  needs 
of  fair  or   moderate  crops. 

878.  In  the   ordinary  cultivation   of  plants   it   is   profitable 
to  augment  in  some  way  the  supply  of  nitrogen  in  most  soils. 
Under  some  circumstances  this  augmentation   can  be  accom- 
plished to  a  certain  extent  by  mere  tillage  or  by  the  exposure 
of  fresh  portions  of  soil  to  the  action  of  the  atmosphere.     But 
it  is  usually  effected  by  the  employment  of  natural  or  artificial 
manures.      The  former  consist  of  the  excrementitious  matters 
of  animals  or  of  the  waste  products  from  plants.     These  ex- 
crementitious matters  represent  a  large  part  of  what  the  ani- 
mals  have   consumed,    and   must    have    come    either    directly 
or  indirectly  from  the  vegetable  kingdom ;  hence  they  only  re- 
store to  the  soil  that  which  plants  had  at  some  time  removed 
therefrom. 

In  the  preparation  of  artificial  fertilizers  an  effort  is  made  to 
provide  for  the  plant  the  mineral  and  nitrogenous  matters  which 
it  requires.  A  large  proportion  of  these  fertilizers  are  composed 

throughout,  and  can  leave  no  doubt  that,  under  the  conditions  of  his  trials, 
there  was  practically  no  utilization  of  the  soil  nitrogen  by  the  plants. 

On  the  other  hand,  experiments  by  Wolff  (Chemisch.-Pharmaceut.  Central- 
Blatt,  1852,  p.  657),  Johnson  (Peat  and  its  Uses,  1866,  p.  79),  and  Storer 
show  that  under  certain  conditions  the  plant  can  avail  itself  of  the  nitrogen 
organically  combined  in  the  soil.  The  works  of  the  above  authors,  which  are 
only  a  few  of  those  bearing  on  this  important  matter,  will  place  the  student  in 
possession  of  the  methods  of  experimenting. 

Storer's  interesting  communication  in  the  Bulletin  of  the  Bussey  Institu- 
tion (vol.  i.,  1874,  p.  252),  "  On  the  Importance  as  Plant-food  of  the  Nitrogen 
in  Vegetable  Mould, >?  gives  not  only  an  account  of  his  experiments  but  also 
a  forcible  presentation  of  the  principal  arguments  in  favor  of  the  belief  that 
the  "soil-nitrogen  "  (that  is,  the  nitrogen  in  vegetable  mould)  is  by  no  means 
inert. 


SYNTHESIS  OF   ALBUMINOUS  MATTERS 


335 


of  a  certain  amount  of  available  calcic  phosphate  together  with 
a  salt  of  potassa  and  some  available  nitrogenous  matter.1 

It  has  been  shown  (p.  248)  that  some  plants  require  more  of 
one  kind  of  food  than  others ;  and  hence  the  attempt  has  been 
often  made  to  prepare  exactly  the  special  fertilizer  which  a  given 
crop  may  require. 

879.  Nitric  acid  and  the  nitrates.     Experiments  with  water- 
culture  have  shown  that  plants  can  derive  all  the  combined  nitro- 
gen needed  for  their  growth  from  nitric  acid  and  the  nitrates. 
But  it  has  also  been  clearly  shown  that  there  are  striking  differ- 
ences in  the  capacity  which  plants  possess  for   appropriating 
nitrogen  from  these  compounds.     Even  in  the  common  agricul- 
tural plants  there  are  some  differences  in  this  respect. 

880.  A  large  number  of  nitrogen   compounds,  such   as   as- 
paragin,  urea,  albumin,  etc.,  have  been  employed  in  experiments 
upon  plants,  but  most  of  the  results  possess  little  interest.     It 
may  be  said,  in  general,  that  the  so-called  alkaloids  (which  con- 
tain nitrogen)  cannot  be  utilized  even  by  the  very  plants  from 
which  they  were  made.2 

881.  Synthesis  of  albuminous  matters  in  the  plant.     A  distinc- 
tion is  made  between  the  newly  formed  or  first-formed  albumi- 
nous substances  in  the  plant  and  those  which  have  undergone 
chemical  changes  in  the  organism,  as  for  instance  the  changes 
in  germination.     Two  views  have  been  held  respecting  the  place 
where  the  formation  of  the  new  protein  matters  occurs  in  the 

1  The  following  analyses,  taken  from  the  Report  of  the  Connecticut  Agri- 
cultural Experiment  Station  for  1883,  indicate  the  composition  of  a  few  such 
substances :  — 


•8  . 

o| 

"32 

g1! 

M 

Is 

2-2 

Phosphoric  acid. 

1 

•— 

ft 

AI 

(Z(  M 

soluble. 

reverted. 

Tobacco  manure  (No.  972). 

1.20 

2.90 

1.21 

7.52 

2.08 

4.35 

"       (No.  965). 

.10 

4.15 

.60 

3.41 

152 

9.03 

Forage  crop  "       (No.  976). 

.21 

.17 

2.91 

6.48 

.77 

4.06 

Potato           "      (No.  905). 

2.59 

.67 

6.87 

.67 

9.76 

For  an  account  of  the  commercial  prices  of  the  available  nitrogen  com- 
pounds for  1883-1884,  see  Report  of  Connecticut  Agricultural  Experiment 
Station,  1885. 

2  For  a  short  account  of  the  bibliography  of  this  subject  the  student  should 
consult  Pfeffer's  Pflanzenphysiologie,  i.,  1881,  p.  242. 


336  ASSIMILATION. 

higher  plants ;  namely,  (1)  that  in  favor  of  the  chlorophyll  cells, 
(2)  that  in  favor  of  the  conductive  tissues  of  the  petiole  and 
stem.  So  far  as  analogy  drawn  from  the  lower  plants  is  con- 
cerned, one  of  these  views  is  as  tenable  as  the  other ;  for  while 
in  a  simple  alga  all  the  formation  of  new  protein  matters  must 
go  on  in  a  cell  where  there  is  chlorophyll  or  its  equivalent,  in 
the  case  of  a  fungus,  nourished  as  in  the  experiments  of  Pasteur 
upon  a  simple  ternary  body  and  a  nitrate,  the  process  must  of 
necessity  take  place  in  cells  where  no  chlorophyll  is  present. 

882.  Exact  observations  upon  the  subject  of  the  formation  of 
albuminous  matters  in  the  plant  are  not  abundant.    Reference  will 
be  made  here  chiefly  to  those  by  Emmerling,  who  carried  on  an 
extended  series  of  investigations  with  Vicia  Faba.    He  examined 
all  parts  of  the  plant  with  respect  to  the  inorganic  nitrogen  com- 
pounds furnished,  and  then  sought  for  the  protein  compounds 
resulting  therefrom.     His  results  are  interpreted  as  showing  that 
the  nitric  acid  which  is  absorbed  from  the  soil,  and  can  be  detected 
in  all  parts  of  the  roots  and  steins,  disappears  very  rapidly  in 
the  leaves  and  all  parts  which  are  actively  growing,  so  that  there 
is  found  only  a  mere  trace  in  them.     According  to  him,  it  is  in 
green  leaves  that  the  transformation  of  nitrogenous  matters  takes 
place.     The  first  product  of  this  transformation  is  not  at  present 
certainly  known  ;  but  there  is  good  reason  to  regard  it  as  a  mem- 
ber of  the  group  of  carbamides.1     Those  parts  of  the  plant  which 
are  rapidly  growing  are  much  richer  in  amides  than  the  older 
and  more   fully  developed   portions.     This   fact   is    shown   by 
Kellner 2  to  be  true  of  pasture  grass,  in  which  the  amides  are 
more  abundant  in  the  young  than  in  the  old  parts. 

APPROPRIATION  OF  SULPHUR. 

883.  The  amount  of  sulphur  which  exists  as  an  essential  part 
of  the  albuminous  matters  of  the  plant  is  quite  small,  being  not 
far  from  one  per  cent.8 

884.  As  already    shown    (681),    sulphur  is   taken   into  the 
plant  in  the  form  of  sulphates,  chiefly  calcic.     The  calcic  sul- 
phate 4  is  probably  decomposed  by  the  oxalic  acid  produced  by 
the  plant,  and  thus  an  insoluble  calcic  oxalate  is  formed ;  then 

1  Versuchs-Stationen,  xxiv.,  1880,  p.  113. 

2  Centralbl.  f.  Agnc.-Chem.,  1879,  p.  271. 

8  Ranging,  according  to  Ebermayer,  from  .4  to  1.8  per  cent  ( Physiologische 
Chemie  der  Pflanzen,  1882,  p.  616). 
*  Holzner :  Flora,  1867. 


APPROPRIATION  OF  ORGANIC   MATTERS.  337 

by  a  process  of  reduction  the  sulphur  is  set  free  to  unite  with  the 
albuminous  matters  already  described. 

The  abundant  occurrence,  in  conducting  tissues  of  stems  and 
petioles,  of  calcic  oxalate  resulting  from  the  changes  described  has 
been  held  to  indicate  the  probable  seat  of  albuminous  synthesis.1 

885.  The  general  statements  which  have  now  been  made  re- 
specting the  appropriation  of  carbon,  nitrogen,  and  sftlphur  hold 
good  for  all  ordinary  land  and  water  plants.     There  are  a  few 
plants,  however,  concerning  which  they  must  be  somewhat  modi- 
fied, and  these  are  here  for  convenience  treated  of  together; 
as  humus-plants,  parasites,  insectivorous  plants,  and  epiphytes. 
It  must  be  remembered  that  in  all  these  apparently  exceptional 
cases  the  mechanism  of  nutrition  is  not  radically  different  from 
that  which  other  plants  possess  at  some  period  of  their  lives 
or  in  some  slight  degree. 

APPROPRIATION  OF   ORGANIC  MATTERS. 

886.  Humus-plants,2  or  Saprophytes.    Among  the  higher  plants 
there  are  some  (for  example,  Epipogium  8)  which  derive  all  their 

1  Sachs  :  Text-book,  2d  Eng.  ed.,  1882,  p.  711. 

2  As  a  matter  chiefly  of  historical  interest,  the  "  humus  theory  "  must  be 
referred  to.     As  stated  in  the  words  of  Liebig,  its  author,  it  is  briefly  as 
follows  :  — 

"  Woody  fibre  in  a  state  of  decay  is  the  substance  called  humus.  .  .  . 
Humus  acts  in  the  same  manner  in  a  soil  permeable  to  air  as  the  air  itself ;  it 
is  a  continued  source  of  carbonic  acid,  which  it  emits  very  slowly.  An  atmos- 
phere of  carbonic  acid,  formed  at  the  expense  of  the  oxygen  of  the  air,  sur- 
rounds every  particle  of  decaying  humus.  The  cultivation  of  land  by  tilling 
and  loosening  the  soil,  causes  a  free  and  unobstructed  access  of  air.  An  atmos- 
phere of  carbonic  acid  is  therefore  contained  in  every  fertile  soil,  and  is  the 
first  and  most  important  food  for  the  young  plants  which  grow  in  it.  ...  The 
roots  perform  the  functions  of  the  leaves  from  the  first  moment  of  their  forma- 
tion :  they  extract  from  the  soil  their  proper  nutriment,  namely,  the  carbonic 
acid  generated  by  the  humus.  .  .  .  When  a  plant  is  quite  matured,  and  when 
the  organs,  by  which  it  obtains  food  from  the  atmosphere,  are  formed,  the  car- 
bonic acid  of  the  soil  is  no  further  required.  .  .  .  Humus  does  not  nourish 
plants  by  being  assimilated  in  its  unaltered  state,  but  by  presenting  a  slow 
and  lasting  source  of  carbonic  acid,  which  is  absorbed  by  the  roots  "  (Chem- 
istry in  its  Application  to  Agriculture,  American  edition,  1842,  pp.  65  et  seq). 

It  has  been  shown  by  the  investigations  referred  to  in  the  text  that  plants 
can  be  grown  with  vigor  and  carried  to  complete  maturity  without  the  supply 
of  .carbonic  acid  to  the  roots,  and  hence  the  "  humus  theory  "  is  emptied  of  all 
its  value ;  but,  as  will  be  shown  later,  the  decaying  vegetable  matter  in  soils 
has  important  functions. 

3  Pfeffer's  Pflanzenphysiologie,  i,  1881,  p.  226. 


338 


ASSIMILATION. 


nutriment  from  the  deca37ing  or  decayed  remains  of  other  plants  ; 
while  others,  like  Monotropa  uniflora  and  the  Orobanchacese,  ob- 
tain part  of  their  food  from  living  plants.  True  parasites  obtain 
their  nourishment  from  living  organisms,  whereas  humus-plants, 
or  saprophytes,  live  upon  the  structures  of  dead  ones.  From  the 
decaying  vegetable  mould  they  procure  all  the  ternary  substances 
needed  for*their  own  fabric,  and  also  the  nitrogenous  substances 
needed  for  their  own  protoplasmic  matters.  It  is  not  known 
exactly  how  saprophytes  turn  to  account  the  comparatively  inert 
nitrogenous  matters  of  vegetable  mould,  but  the  process  is  thought 
to  depend  upon  the  action  of  a  solvent,  unorganized  ferment, 
somewhat  similar  to  that  which  effects  changes  in  the  food  within 
reach  of  the  embryo  of  the  seed. 

887.  Parasites  obtain  a  large  part  of  their  food  from  living 

organisms.  In  some  cases  they 
appear  to  be  able  thus  to  procure 
all  the  food  they  require  ;  but  most 
of  them  can  be  shown  to  elaborate, 
by  means  of  the  small  amount  of 
chlorophyll  which  they  possess,  a 
small  part  of  their  food.  The 
haustoria,  by  means  of  which  they 
abstract  from  other  plants  the  as- 
similated matters,  have  been  de- 
scribed in  351.  After  the  parasite 
has  fairly  fastened  itself  upon  the 
host-plant,  it  acts  with  respect  to 
the  tissues  of  the  latter  much  as  if 
it  were  an  offshoot  of  the  host.  It 
appropriates  the  assimilated  matters 
as  they  are  needed,  and  consumes 
them  in  substantially  the  same  way 
that  an  embryo  consumes  the  food  stored  in  the  endosperm.1 

888.  Insectivorous  or  carnivorous  plants,  as  already  explained 
in  Volume  I.  page  110,  et  seq.,  are  those  which  are  provided  with 
some  specialized  apparatus  for  the  utilization  of  animal  matters. 

1  For  an  interesting  account  of  the  more  striking  effects  produced  upon  the 
host-plant,  the  reader  should  consult  Frank  :  Die  Pflanzenkrankheiten,  1879. 

The  relations  which  exist  between  the  ash-constituents  of  the  parasite  and 
Its  host  have  been  examined  by  Reinsch. 

FIG.  152.  Cuscuta,  a  parasite.  The  colled  embryo  and  seedling  are  shown  In  the 
right-hand  sketches;  in  the  other  sketch,  the  adult  plant,  with  its  flower-clusters,  at- 
tached to  the  living  stem  of  another  plant. 


DROSERA   ROTUNDIFOLIA. 


339 


The  structure  and  office  of  the  prehensile  and  digestive  appara- 
tus are  now  to  be  illustrated  by  the  following  examples  :  — 

889.  Drosera    rotundifolia,    or   round-leaved   sundew,    grows 
abundant!}'  in  northern  peat-bogs  and  in  sand  mixed  with  vege- 
table mould,  both  in  the  Old  World  and  the  New.     The  plant 
has  a  few  (4  to  12)  leaves,  arranged  in  a  flat  tuft  at  the  base  of 
the  flower-stalk,  and  narrowed  at  their  bases  into  hairy  petioles. 
The  most  striking  character  of  the  leaves  is  the  thick  clothing 
of  peculiar  hairs,  otherwise  known  as  tentacles  or  glands,  from 
the  tip   of  each   of  which  exudes  a  drop  of  a  clear  viscid 
liquid.     These  hairs  are  complicated 

in  structure.  They  contain  all  the 
histological  elements  proper  to  the 
leaf  itself;  for  this  reason  it  has  been 
thought  by  some  that  they  should  be 
regarded  as  processes  from  the  leaf 
rather  than  as  hairs.  The  marginal 
tentacles  are  long,  have  purple  stalks, 
and  are  terminated  by  elongated  pur- 
ple glands  ;  those  towards  the  middle 
of  the  leaf  are  shorter,  have  greenish 
stalks  and  ovoid  glands.  Each  gland 
consists  of  a  double  layer  of  polygo- 
nal cells  which  surround  a  central 
bod}r  composed  of  elongated  cells 
and  a  few  tracheids.  The  proto- 
plasmic lining  of  all  the  cells  is  transparent  and  thin,  and  the 
cavity  is  filled  with  an  homogeneous  purple  fluid.  The  tra- 
cheids pass  by  insensible  gradations  into  minute  spiral  ducts. 

890.  The  mode  of  action  in  Drosera  is  as  follows :  When 
a  small  object  is  placed  on  the  middle  glands,  a  sluggish  move- 
ment is  soon  detected  in  the  marginal  tentacles.     If  the  object 
is  a  fragment  of  animal  matter,  the  motor  impulse  is  commu- 
nicated rapidly,  and  the  marginal  tentacles  curve  sharply  over 
upon  the  fragment,  bringing  the  glands  in  contact  with  it.     The 
blade  of  the  leaf  also  sometimes  becomes  curved,  forming  a  shal- 
low cup.     Inorganic  and  such  organic  matters  as  are  not  acted 
on  by  the  secretion  from  the  glands  act  more  slowly  in  causing 
movement  of  the  tentacles  than  do  soluble  organic  substances, 
and   no    movement   follows   unless   the   object   rests   upon  the 
glands  themselves,  not  merely  on  the  secretion  which  covers 


FIG.  153.    Drose-a  rotnndifolia.    View  of  leaf  from  above.    (Darwin.) 


340  ASSIMILATION, 

them.     Darwin  found  that  movement  was  caused  by  the  contact 
of  a  particle  weighing  only  .0008  milligram  (7?fjTr  of  a  grain). 

When  a  tentacle  has  been  excited  by 
contact  with  a  solid  particle,  there  is  seen, 
aftef  some  hours,  a  remarkable  change  in 
its  cells  near  the  gland.  "Instead  of  be- 
ing filled  with  homogeneous  purple  fluid, 
they  now  contain  variously  shaped  masses 
of  purple  matter  suspended  in  a  colorless  or 
almost  colorless  fluid." 1  Tentacles  which 
have  been  thus  acted  on  by  contact  of  par- 
ticles have  a  mottled  appearance,  and  can 
be  picked  out  with  ease  from  all  the  others. 
The  change  of  contents  is  termed  by  Darwin 
aggregation.  "  The  little  masses  of  aggre- 
gated matter  are  of  the  most  diversified 
shapes,  often  spherical  or  oval,  sometimes  much  elongated,  or 
quite  irregular  with  thread  or  necklace-like  or  club-formed  pro- 
jections. They  consist  of  thick,  apparently  viscid  matter,  which 
in  the  exterior  tentacles  is  of  a  purplish,  and  in  the  short  discal 
tentacles  of  a  greenish,  color.  These  little  masses  incessantly 
change  their  forms  and  positions,  being  never  at  rest.  .  .  . 

"  Shortly  after  the  purple  fluid  within  the  cells  has  become 
aggregated,  the  little  masses  float  about  in  a  colorless  or  almost 
colorless  fluid  ;  and  the  layer  of  white  granular  protoplasm  which 
flows  along  the  walls  can  now  be  seen  much  more  distinct!}*. 
The  stream  flows  at  an  irregular  rate,  up  one  wall  and  down  the 
opposite  one,  generally  at  a  slower  rate  across  the  narrow  ends 
of  the  elongated  cells,  and  so  round  and  round.  But  the  current 
sometimes  ceases.  The  movement  is  often  in  waves,  and  their 
crests  sometimes  stretch  almost  across  the  whole  width  of  the 
cell  and  then  sink  down  again.  Small  spheres  of  protoplasm, 
apparently  quite  free,  are  often  driven  by  the  current  round  the 
cells ;  and  filaments  attached  to  the  central  masses  are  swayed 
to  and  fro,  as  if  struggling  to  escape.  Altogether,  one  of  these 
cells,  with  the  ever-changing  central  masses  and  with  the  Ia3'er 
of  protoplasm  flowing  round  the  walls,  presents  a  wonderful 
scene  of  vital  activity." 2 

1  Darwin :  Insectivorous  Plants,  1875,  p.  39. 

2  Darwin  :  Insectivorous  Plants,  pp.  40,  42. 

Fia.  154.  Drosera  rotundifolia.  Leaf  with  the  tentacles  on  ono  side  inflected  over  a 
bit  of  meat  placed  on  the  disc.  (Darwin.) 


t>ROSEBA  ROTUNDIFOLIA.  341 

The  aggregation  is  caused  by  various  nitrogenous  organic 
fluids  and  salts  of  ammonia  ;  the  most  efficient  agent  for  its  pro- 
duction being  ammonic  carbonate,  .000482  milligram  (73^^  of 
a  grain)  being  enough  to  cause  aggregation  in  all  the  cells  of  a 
tentacle.  These  figures  show  the  extreme  sensitiveness  of  the 
tentacles  and  glands  to  slight  external  impressions. 

891.  "If  the  glands  are  excited  either  by  the  absorption  of 
nitrogenous  matter  or  by  mechanical  irritation,  their  secretion 
increases  in  quantity  and  becomes  acid."     That  it  contains  an 
unorganized  ferment  admits  of  no  question.     The  secretion  after 
excitation  possesses  the  power  of  dissolving  the  albuminoids  sub- 
stantially as  the  gastric  juice  of  animals  does.     When  an  insect 
alights  upon  the  leaf  of  Drosera,  its  violent  struggles  to  escape 
only  wind  more  closely  about  it  the  threads  of  viscid  matter 
from  the  glands.     Soon  the  tentacles  close  around  it,  and  the 
increased  secretion  of  the  digestive  fluid  brings  about  a  true 
digestion  of  the  nitrogenous  matter. 

892.  That  the  digested  matters  can  be  absorbed,  appears  from 
numerous  experiments.     In  these,   after  the  disappearance   of 
albuminous  matters  impregnated  with  a  salt  of  lithium,  it  was 
possible  with  the  spectroscope  to  detect  the  salt  in  the  plant. 
Parts  of  the  leaves  remote  from  the  seat  of  digestion,  being 
dried,  calcined,  moistened  with  hydrochloric  acid,  and  placed  in 
the  colorless  flame  of  a  Bunsen  burner,  gave  the  characteristic 
lithium  line. 

893.  Does  the  plant  gain  any  advantage  by  this  absorption 
of  organic  matter?     Francis  Darwin's1  experiments  upon  this 
subject  may  be  briefly  stated  as  follows :  — 

Two  sets  of  thrifty  plants  of  Drosera  were  cultivated  under 
the  same  conditions,  with  the  single  exception  of  a  provision  of 
animal  food  to  the  leaves  of  one  set.  At  the  conclusion  of  an 
experiment  extending  through  three  months,  the  ratios  between 
the  unfed  and  the  fed  plants  were  as  follows :  — 

Unfed.     Fed. 
Weight  of  plants,  exclusive  of  flower-stems    ....     100      121.5 

Number  of  flower-stems 100      164.9 

Total  weight  of  flower-stems 100      231.9 

Total  number  of  capsules 100      194.4 

Average  weight  per  seed 100      157.3 

Total  calculated  number  of  seeds  produced     ....     100:241.5 
Total  calculated  weight  of  seeds 100  :  379.7 

1  Journal  of  the  Linnaean  Society,  xvii.,  1880,  p.  17. 

"  Two  hundred  plants  of  Drosera  rotundifolia  were  transplanted  in  June  and 
cultivated  in  soup-plates  filled  with  moss  during  the  rest  of  the  summer.  Each 


342 


ASSIMILATION. 


894.  Dioiiaea  muscipnla,  or  Venus's  fly-trap,  grows  sparingly 
in  sandy  soil  near  Wilmington,  North  Carolina,  and  in  one  or 
two  other  localities  along  the  Carolina  coast.  Its  leaf  consists  of 
two  rather  distinct  parts,  —  the  two-valved  trap  at  the  extremity, 


and  a  petiole-like  support.  It  is  probable  that  the  support  is  not 
a  true  petiole,  but  a  leaf-blade,  while  the  trap  is  a  special  ap- 
pendage developed  upon  the  tip  of  the  leaf-blade. 

895.    The  spring-trap  is  made  up  of  two  symmetrical  halves 
meeting  at  a  median  hinge.     The  outer  border  of  each  half  is 


plate  was  divided  into  halves  by  a  low  wooden  partition,  one  side  being  des- 
tined to  be  fed  with  meat,  while  the  plants  in  the  opposite  half  were  to  be 
starved.  The  plates  were  placed  altogether  under  a  gauze  case,  so  that  the 
'starved'  plants  might  be  prevented  from  obtaining  food  by  the  capture  of 
insects.  The  method  of  feeding  consisted  in  supplying  each  leaf  (on  the  fed 
sides  of  the  six  plates)  with  one  or  two  small  bits  of  roast  meat,  each  weighing 
about  one-fiftieth  of  a  grain.  This  operation  was  repeated  every  few  days  from 
the  beginning  of  July  to  the  first  days  of  September,  when  the  final  comparison 
of  the  two  sets  of  plants  was  made  "  (Nature,  xvii.,  1878,  p.  223). 

FIG.  155.    A  plant  of  Dionaea  muscipula,  reduced  in  size. 

FIG.  156.    Three  of  the  leaves  of  almost  the  natural  size ;  one  of  them  open,  the 
others  closed.    Probably  a  fly  is  never  caught  by  the  teeth  as  here  represented. 


DION^A   MUSCIPULA.  343 

fringed  with  stiff  bristles  so  placed  as  to  interlock  when  the  trap 
is  shut.  The  upper  face  of  each  half  is  somewhat  convex  when 
the  trap  is  open,  and  upon  it  there  are  three  delicate  hairs  which 
are  exceedingly  sensitive.  Supposing  the  plant  to  be  in  health 
and  under  favorable  conditions,  the  lightest  touch  upon  one  of 
the  hairs  upon  the  face  of  the  trap  will  cause  the  valves  to  close 
instantly,  bringing  their  edges  in  apposition.  A  light  touch  in 
the  median  line,  that  is,  at  the  hinge,  will  produce  the  same 
effect.  The  sensitive  hairs  each  consist  of  several  rows  of  elon- 
gated cells  so  arranged  as  to  form  a  conical  filament  resting  on 
a  constricted  base  and  attached  by  an  articulation  to  a  rounded 
group  of  cells.  This  structure  enables  the  hairs  to  bend  when 
the  trap  is  shut. 

896.  The   digestive   apparatus   consists-  of   minute    reddish 
short-stalked  glands  made  up  of  a  few  polyhedral  cells.     These 
do  not  secrete  any  fluid  unless  excited  by  the  presence  of  food- 
materials,  when  they  secrete  copiously  a  colorless,  glair}',  acid 
liquid,  containing  an  unorganized  ferment  similar  to  that  produced 
by  the  stomach  of  animals,  if  not  identical  with  it.     Scattered 
among  the  secretory  glands  are  numerous  compound  hairs  formed 
of  eight  divergent  cells,  which  are  generally  orange  or  brown 
in  color. 

897.  From  experiments  by  Darwin  and  others  it  is  clear  that 
dry  albuminous  solids  do  not  excite  the  action  of  the  glands,  but 
if  moistened  very  slightly,  they  call  the  glands  into  activity. 
Moreover,  if  the  bit  of  meat  or  other  albuminous  matter  be 
placed  on  the  valves  in  such  a  way  as  not  to  spring  the  trap,  the 
valves  will  soon  slowly  close  without  further  touch.     Aggrega- 
tion takes  place  in  the  cells  of  the  glands  in  much  the  same  way 
as  in  Drosera. 

898.  When  a  small  insect  is  caught  by  the  springing  of  the 
trap,  it  can  escape  after  a  time  through  the  spaces  left  between 
the  bristles  at  the  border ;  but  if  the  insect  is  of  moderate  size, 
its  escape  is  impossible :  the  valves  shut  down  more  and  more 
tightly  upon  it,  and  digestion  soon  begins. 

899.  The  opening  of  the  valves  after  digestion  takes  place  in 
different  times  according  to  the  vigor  of  the  plant  and  nature 
of  the  prey.    After  a  mere  touch  by  which  the  trap  is  sprung 
without  anything  in  it,  the  valves  will  again  open  of  themselves 
in  a  day  or  even  less.     When  the  trap  is  closed  by  a  bit  of  meat, 
the  valves  open  in  from  three  or  four  days  to  rather  more  than 
a  week  ;  when  it  closes  over  a  large  insect,  they  remain  shut  for 
a  much  longer  time,  even  for  a  month. 


344  ASSIMILATION. 

900.  Canby1  states  that  he  has  known  "vigorous  leaves  to 
devour  their  prey  several  times ;  but  ordinarily  twice,  or  quite 
often  once,  was  enough  to  render  them  unserviceable."     Mrs. 
Treat1  observes  that  "  several  leaves  caught  successively  three 
insects  each,  but  most  of  them  were  not  able  to  digest  the  third 
fly,  but  died  in  the  attempt.      Five  leaves,  however,  digested 
each  three  flies  and  closed  over  the  fourth,  but  died  soon  after 
the  fourth  capture.    Many  leaves  did  not  digest  even  one  large 
insect." 

901.  The  following  experiments  by  Darwin  illustrate  the  flow 
of  the  secretion:   "A  bit  of  albumin  T'ff  of  an  inch  square  but 
only  J$  in  thickness,  and  a  piece  of  gelatin  £  inch  long  and  ^ 
broad,  were  placed  on  a  leaf  which  eight  days  afterwards  was 
cut  open.     The  surface  was  bathed  with  slightly  adhesive  acid 
secretion,  and  the  glands  were  all  in  an  aggregated  condition. 
Not  a  vestige   of  the  albumin   or  gelatin  was  left.     Similarly 
sized  pieces  were  placed,  at  the  same  time,  on  wet  moss  in  the 
same  pot,  so  as  to  be  subjected  to  nearly  similar  conditions ; 
after  eight  days  these  were  brown,  decayed,  and  matted  with 
fibres  of  mould,  but  had  not  disappeared."  2 

902.  That  the  digested  matters  are  absorbed  by  the  leaf  has 
been  shown  by  the  spectroscope,  as  in  the  case  of  Drosera ;  but 
no  experiments  are  yet  on  record  as  to  the  effect  of  this  nutritive 
matter  on  the  plant. 

The  character  of  the  movement  by  which  the  trap  is  sprung  is 
spoken  of  in  the  chapter  on  ' '  Movements." 8 

903.  Other  insect-catching  Droseraceae.     Drosera  and  Dionaea 
are   members  of   the   order  Droseraceae.      Its   four   remaining 
genera  have  also  the  power  of  capturing  insects. 

Aldrovanda  has  been  well  called  a  miniature  Dionaea.  Its 
bilobed  leaves  float  in  water  (the  plant  being  destitute  of  roots) . 
Each  leaf  is  two-valved,  something  after  the  fashion  of  Dionaea, 
but  each  valve  is  made  up  of  two  parts.  One,  near  the  hinge 
in  the  median  line,  is  provided  with  colorless  glands ;  the 
other,  a  sort  of  thin  film  outside,  has  no  true  glands.  On 
the  inner  part  there  are  some  extremely  delicate  hairs  which 

1  Cited  by  Darwin  :  Insectivorous  Plants,  1875,  p.  311. 

2  Insectivorous  Plants,  p.  302. 

8  Bunion  Sanderson  has  investigated  the  electrical  disturbance  which  takes 
place  when  the  trap  of  Dionaea  is  sprung.  For  details  and  conclusions  see  the 
following  papers  :  Proceedings  of  the  Royal  Society,  vol.  xxi.  p.  495,  and  Na- 
ture, x.,  1874,  pp.  105,  127.  But  similar  electrical  disturbances  are  exhibited 
when  any  fresh  vegetable  structure  is  sharply  bent. 


PINGUICULA.  345 

have  been  shown  to  be  sensitive,  and  on  touching  them  the 
valves  close.  By  this  plant  minute  water-insects  and  crusta- 
ceans are  captured  (see  Fig.  190). 

Drosophyllum,  a  rare  plant  found  in  Portugal,  catches  insects 
by  a  viscid  secretion  from  minute  mushroom-shaped  glands. 
The  tentacles  do  not  have  the  power  of  movement  possessed 
by  those  of  Drosera.  That  its  glands  can  secrete  a  digestive 
fluid  appears  from  Mr.  Darwin's  experiments. 

Roridula,  found  at  the  Cape  of  Good  Hope,  and  Byblis,  of 
western  Australia,  closely  resemble  the  viscid-haired  Droseraceae, 
which  have  been  examined  in  a  fresh  state,  and  they  have  been 
added  to  the  list  of  the  insect-catching  plants  of  the  order. 

904.  Pinguicula  is  so  called  from  the  greasy  appearance  pre- 
sented by  the  upper  surface  of  its  leaf,  due  to  the  existence  of 
great  numbers  of  disc-like  glandular  hairs  with  short   stalks. 
The  glandular  character  of  the  hairs  is  shown  by  the  secretion 
which  exudes  from  them  even  when  they  are  not  irritated. 

905.  The  secretion  which  flows  when  the  leaves  of  Pinguicula 
are  not  excited  by  the  presence  of  albuminous  matter  is  neutral ; 
but  upon  excitation  of  the  leaf  it  becomes  acid,  far  more  copious 
in  amount,  and  has  the  power  of  digesting  nitrogenous  organic 
substances.     At  that  time  the  clear  contents  of  the  cells  of  the 
glands  also  become  aggregated,  much  as  in  the  case  of  the  cells 
in  Drosera  ;  and  this  fact  is  adduced  by  Darwin  as  proof  that  the 
digested  matters  are  absorbed. 

906.  In   about   three  hours  after  an  insect 
alights  upon  a  leaf  of  Pinguicula  the  margin 
begins  to  roll  over  it  and  envelop  it,  in  the 
manner   shown    by   the    accompanying   figure. 
The    following   experiment   by    Darwin   shows 
what  takes  place  in  this  incurving:  "A  young 
and  almost  upright  leaf  was  selected  with  its 
two  lateral  edges  equally  and  very  slightly  in- 
curved.    A  row  of  small  flies  was  placed  along 
one  margin.     When  looked  at  next  day,  after 
fifteen  hours,  this  margin  but  not  the  other  was 
found  folded  inwards,  like  the  helix  of  the  human 
ear,  to  the  breadth  of  one  tenth  of  an  inch,  so 
as  to  lie  partly  over  the   row  of  flies.      The 

glands  on  which  the  flies  rested,  as  well  as  those  on  the  over- 


Fio.  157.    Pinguicula  vulgaris.    Outline  of  leaf  with  its  left  margin  inflected  over  a. 
row  of  small  flies.    (Darwin . ) 


346  ASSIMILATION. 

lapping  margin  which  had  been  brought  into  contact  with  the 
flies,  were  all  secreting  copiously." l 

The  incurvation  lasts  for  only  a  day  or  two,  after  which  the 
leaf  assumes  its  former  position  :  fragments  of  glass  keep  the  mar- 
gins incurved  for  a  shorter  time  than  do  nitrogenous  bodies.2 

907.  Darwin  suggests  the  two   following  advantages  which 
the  plant  can   derive  from  even  this  transient  inrolling:    (1) 
the  captured  food  and  the  secretion  are  protected  from  rain, 
and   (2)  the  food  is  brought  into  contact  with  a  larger  number 
of  glands  than  if  the  leaf  remained  flat. 

908.  It  appears  probable  that  the  leaves  of  Pinguicula  derive 
some  nourishment  from  the  seeds,  etc.,  which  may  fall  upon  them. 
"We  may  therefore  conclude  that  Pinguicula  vulgaris,  with  its 
small  roots,  is  not  only  supported  to  a  large  extent  by  the  extraor- 
dinary number  of  insects  which  it  habitually  captures,  but  like- 
wise draws  some  nourishment  from  the  pollen,  leaves,  and  seeds 
of  other  plants  which  often  adhere  to  its  leaves.     It  is  therefore 
partly  a  vegetable  as  well  as  an  animal  feeder." 8 

909.  Utricnlaria,  a  genus  named  from  the  utriculi  or  little 
bladders  found  on  the  dissected  leaves  of  some  of  its  species, 
belongs  to  the  same  natural  order  as  Pinguicula.     Its  members 
capture  minute   aquatic   animals  by  means   of  peculiar  traps. 
Each  bladder  has  at  its  mouth  a  few  diverging  hairs,  while  just 
within  the  orifice  there  is  a  sort  of  trap-door,  which  can  be  lifted 
by  a  slight  touch  and  then  falls  by  its  own  weight,  covering  the 
mouth  and  preventing  egress.     If  a  small  aquatic  animal  passes 
through  the  entrance  and  pushes  by  the  funnel-shaped  trap-door, 
it  is  securely  imprisoned.     The  interior  of  the  bladders  is  lined 
more  or  less  thickly  with  peculiar  glandular  hairs  not  very  unlike 
those  intermingled  with  the  glands  of  Drosera,  and  found  also  on 
the  valves  of  Dionaea.     These  are  either  bifid  or  quadrifid. 

910.  According  to  Darwin  these  hairs  have  the  power  of  ab- 
sorbing dissolved  matters  in  a  state  of  decay,  but  there  is  in 
them  no  true  digestive  capacity.     If  the  plants  can  utilize  ani- 
mal matter  at  all,  it  is  only  after  it  has  become  dissolved  during 
the  process  of  decay. 

911.  Genlisea.     The  plants  belonging  to  the  genus  Genlisea 
—  a  genus  allied  to  Utricularia  —  have  two  kinds  of  leaves,  ordi- 
nary and  bladder-bearing,  and  the  bladders  have  something  of 
the  same  arrangement  at  the  orifice  as  has  already  been  alluded 
to  under  Utricularia. 

1  Insectivorous  Plants,  p.  371.  3  Insectivorous  Plants,  p.  390. 

2  Insectivorous  Plants,  p.  377. 


SARRACENIA. 


347 


912.  Sarraccnla.  All  of  the  eight  species  of  this  genus  have 
hollowed  phyllodia,  which  form  slender  pitchers  or  urns.  In  the 
best-known  species,  S.  purpurea,1  the 
urn  is  generally  so  held  that  rain  can 
fall  directly  into  it ;  in  fact,  the  upright 
foliar  expansion  would  seem  to  insure 
that  none  be  lost.  In  S.  flava,  Druin- 
mondii,  and  rubra,  the  pitchers  are 
more  nearly  vertical,  and  the  lid  at  the 
mouth  of  the  tube  so  disposed  when 
the  leaf  is  young  as  to 
shed  for  the  most  part 
rain  that  falls  thereon  ; 
but  in  the  older  leaves 
the  lid  becomes  some- 
what erect.  Even  in 
the  latter  position  a  por- 
tion of  the  rain  that  falls 
upon  the  leaves  is  car- 
ried off.  In  the  re- 
maining species,  S.  variolaris  and  psittacina,  the 
lid  is  a  roof  which  keeps 
the  rain  from  entering  the 
tube.  In  all  the  cases  there 
is  usually  considerable  water 
in  the  pitchers ;  in  the  last 
two  species  it  probabty  all 
comes  from  within  as  a  se- 
cretion. 

913.  Sarracenia  variolaris 
has  been  long  known  to  at- 
tract insects  to  the  leaves. 
Passing  over  the  earlier  no- 
tices referred  to  in  the  Bib- 
liography, page  351,  the 
following  quotation  from 
MacBride,2  written  in  1815,  will  indicate  sufficiently  the  char- 
acter of  the  attraction  :  — 


1  Schimper:  Botauische  Zeitung,  1882,  p.  225. 

2  Transactions  of  the  Linnrean  Society,  xii.,  1818,  p.  48. 

FIG.  158.    Pitcher-leaves  of  Sarracenia  purpurea ;  one  has  the  upper  part  cut  away. 
FIG.  159.    Pitcher  of  Sarracenia  variolaris. 
FIG.  160.    Pitcher  of  Sarracenia  psittacina. 


348  ASSIMILATION. 

"  The  cause  which  attracts  flies  is  evidently  a  viscid  substance, 
resembling  honey,  secreted  by  or  exuding  from  the  internal  sur- 
face of  the  tube.  From  the  margin  where  it  commences,  it  does 
not  extend  lower  than  one  fourth  of  an  inch.  The  falling  of  the 
insect  as  soon  as  it  enters  the  tube  is  wholly  attributable  to  the 
downward  or  inverted  position  of  the  hairs  of  the  internal  surface 
of  the  leaf.  At  tne  bottom  of  the  tube,  split  open,  the  hairs  are 
plainly  discernible,  pointing  downwards ;  as  the  eye  ranges  up- 
ward they  gradually  become  shorter  and  attenuated,  till  at  or 
just  below  the  surface  covered  with  the  bait,  they  are  no  longer 
perceptible  to  the  naked  eye  nor  to  the  most  delicate  touch.  It 
is  here  that  the  fly  cannot  take  a  hold  sufficiently  strong  to  sup- 
port itself,  but  falls." 

914.  The  tissues  of  the  internal  surfaces  of  the  pitchers  have 
been  classified  by  Hooker  in  the  following  manner :  — 

"  (1)  An  attractive  surface,  occupying  the  inner  surface  of 
the  lid,  which  possesses  stomata,  and  (in  common  with  the 
mouth  of  the  pitcher)  minute  honey-secreting  glands ;  it  is, 
further,  often  more  highly  colored  than  any  other  part  of  the 
pitcher,  in  order  to  attract  insects  to  the  honey. 

"  (2)  A  conducting  surface,  which  is  opaque,  formed  of 
glassy  cells,  which  are  produced  into  deflexed,  short,  conical 
processes.  These  processes,  overlapping  like  the  tiles  of  a 
house,  form  a  surface  down  which  an  insect  slips,  and  affords 
no  foothold  to  one  attempting  to  crawl  up  again. 

"  (3)  A  glandular  surface  (seen  in  S.  purpurea),  which  occu- 
pies a  considerable  portion  of  the  cavity  of  the  pitcher  below  the 
conducting  surface.  It  is  formed  of  a  layer  of  epidermis  with 
sinuous  cells,  and  is  studded  with  glands.  Being  smooth  and 
polished,  this,  too,  affords  no  foothold  for  escaping  insects. 

"  (4)  A  detentive  surface,  which  occupies  the  lower  part  of  the 
pitcher,  in  some  cases  for  nearly  its  whole  length.  It  possesses 
no  cuticle,  and  is  studded  with  deflexed,  rigid,  glass-like,  needle- 
formed  hairs,  which  further  converge  towards  the  axis  of  the 
diminishing  cavity  ;  so  that  an  insect,  if  once  amongst  them,  is 
effectually  detained,  and  its  struggles  have  no  other  result  than 
to  wedge  it  lower  and  more  firmly  in  the  pitcher." 

915.  Mellichamp  describes  a  line  of  saccharine  liquid  which 
leads  up  from  the  base  of  the  leaf  to  its  brim.     This  secretion 
comes  from  glands  at  the  mouth  of  the  pitcher ;  but  it  is  found 
only  at  certain  periods.     Led  by  this  lure,  insects  are  drawn 
towards  the  brim  of  the  pitcher,  and  sooner  or  later  they  are 
caught  in  considerable  numbers  in  the  pitchers  themselves. 


NEPENTHES. 


349 


916.  The  exact  nature  of  the  liquid  in  the  pitchers  is  not  fully 
understood.      Mellicharnp's  observations  seem  to  indicate  that 
it  has  the  power  of  accelerating  the  decomposition  of  animal 
matter.     Nothing  is  yet  known  positively  as  to  the  manner  in 
which  the  products  of  decomposition  are  utilized  by  the  plant, 
if,  indeed,  they  are  at  all  serviceable  to  it.1 

917.  Darliiigtonia  has   been    examined 
by  Canby,    who    finds   strong   indications 
that  it  allures  insects  much  as  the  Sarra- 
cenias  do. 

918.  Nepenthes.    This  striking  plant  has 

long  been  a  favor- 
ite in  the  green- 
house on  account 
of  its  peculiar 
leaves,  which  often  combine 
a  blade,  a  tendril,  and  a  well- 
formed  urn.  The  species  of 
Nepenthes  (about  thirty  in 
number)  produce  pitchers  at 
the  extremity  of  their  tendril- 
like  leaves.  When  the  plants 
are  young  these  pitchers  are 
less  elongated  and  are  apt  to 
rest  on  the  ground,  and  in 
such  plants  their  whole  inte- 
rior is  clothed  with  secreting  glands. 
When  the  plant  is  older,  the  pitchers 
become  more  distinctly  tubular,  and  do 
not  possess  such  conspicuous  wings  as  those  found  in  the  form 
just  mentioned.  All  of  them  have  lids ;  in  one  case  the  lid  is 

1  It  is  interesting  to  observe  some  of  the  early  conjectures  as  to  the  probable 
use  of  these  pitchers.  "  Morrison  speaks  of  the  lid,  which  in  all  the  species  is 
tolerably  rigidly  fixed,  as  being  furnished  by  Providence  with  a  hinge.  This 
idea  was  adopted  by  Linnaeus,  and  somewhat  amplified  by  succeeding  writers, 
who  declared  that  in  dry  weather  the  lid  closed  over  the  mouth  and  checked 
the  loss  of  water  by  evaporation.  Catesby,  in  his  fine  work  on  the  '  Natural 
History  of  Carolina,'  supposed  that  these  water-receptacles  might  '  serve  as  an 
asylum  or  secure  retreat  for  numerous  insects,  from  frogs  and  other  animals 
which  feed  on  them  ;'  and  others  followed  Linnreus  in  regarding  the  pitchers 
as  reservoirs  for  birds  and  other  animals,  more  especially  in  times  of  drought " 
(Hooker's  Address  before  British  Association,  1874).  But  Burnett  regarded 
the  tubes  as  closely  analogous  to  the  stomachs  of  animals. 

Fia.  161.    Pitcher  of  Darlingtonia  Califoniica. 

FIG.  162.    Leaf  of  Nepenthes;  leaf,  tendril,  and  pitcher  combined. 


350  ASSIMILATION. 

thrown  back,  but  in  the  others  its  overarching  is  a  conspicuous 
feature.  The  mouth  of  the  pitcher  is  strengthened  by  a  thick 
rim,  near  which  are  very  numerous  glands  secreting  a  sweet 
liquid.  In  the  interior  of  the  pitcher  there  is  a  conductive  sur- 
face, somewhat  like  that  seen  in  Sarracenia.  This  extends  for 
some  distance  down  from  the  mouth,  and  is  frequently  crowned 
by  a  sort  of  funnel-like  appendage  of  the  rim.  Below  the  con- 
ductive surface  there  is  a  secreting  surface  dotted  with  innu- 
merable glands.  According  to  Hooker,  from  whose  notice  many 
of  the  facts  here  given  are  taken,  there  are  three  thousand  of 
these  glands  in  a  square  inch. 

The  fluid  which  collects  in  the  pitchers  has  been  shown  by 
Gorup-Besanez  and  Will  to  be  neutral,  or  only  very  slightly  acid 
in  reaction,  unless  animal  matter  has  been  introduced.  If,  how- 
ever, any  animal  matter  has  been  placed  in  the  pitchers,  the 
glands  give  forth  an  acid  secretion,  which  contains  an  active 
ferment  that  resembles  pepsin  and  has  the  power  of  digesting 
albuminous  substances.  It  is  an  interesting  fact  that  the  neutral 
secretion,  although  it  has  not  the  power  of  digesting  albuminous 
matters,  becomes  efficient  at  once  upon  the  addition  of  a  small 
amount  of  acid  (formic).  During  digestion  the  glands  exhibit 
the  same  phenomena  of  aggregation  as  observed  in  Drosera. 

The  absorption  of  animal  matter  by  Nepenthes  has  been 
proved  by  the  Lithium  method. 

919.  By  the  viscid  or  glandular  hairs  of  a  large  number  of 
plants  insects  are  sometimes  caught,  but  to  what  extent  these 
hairs  serve  in  digestion  and  absorption  is  not  yet  clear.     From 
experiments  by  Darwin,  it  appears  that  in  some  cases  at  least 
they  may  aid  the  plant  in  absorbing  ammonia  compounds  found 
in  rain  and  in  the  atmosphere,  and  that  the  glands  ma}-  also 
"obtain  animal  matter  from  the  insects  which  are  occasionally 
entangled  by  the  viscid  secretion."1    One  case  merits  particular 
attention  ;  namety,  that  of 

920.  Dipsacns,  or  Teasel.     Francis  Darwin  has  called  atten- 
tion to  the  extraordinary  character  of  some  of  the  hairs  of  this 
plant.     The  following  abstract  gives  only  the   briefest   outline 
of  his  interesting  paper. 

The  glandular  hairs  are  multicellular  and  pear-shaped,  being 
supported  by  the  small  end  on  a  cylindrical  stalk,  which  rests  on 
an  epidermal  cell.  At  the  summit  of  the  gland  where  several  of 

1  Darwin:  Insectivorous  Plants,  p.  355.  The  catchfly  (Silene)  should  be 
examined  with  reference  to  this  point. 


DIPSACTJS.  351 

the  radiating  cells  meet,  threads  of  gelatinous  matter  can  be  seen 
to  protrude  under  certain  circumstances.  No  apertures,  how- 
ever, can  be  seen  through  which  the  filaments  come,  therefore 
it  is  thought  that  they  extend  directly  through  the  cell-walls. 
They  have  been  shown  to  consist  of  protoplasmic  matter  with 
which  a  certain  amount  of  resinous  substance  is  combined,  and 
at  times  they  contract  violently,  become  thicker,  and  at  last 
form  a  small  ball  on  the  summit  of  the  gland.  The  contraction 
can  be  produced  by  man}-  chemical  and  physical  agents,  e.  </., 
ammonic  carbonate.  If  a  filament  under  the  microscope  is 
treated  with  a  drop  of  a  2  per  cent  solution  of  the  carbonate,  the 
following  changes  occur :  The  filament  contracts,  but  almost 
instantly  recovers  itself,  and  is  once  more  protruded ;  it  does 
not,  however,  regain  its  original  form  or  appearance  ;  instead  of 
consisting  of  thin  elongated  ropes  of  a  highly  refracting  sub- 
stance, it  is  converted  into  necklace-like  masses  which  strongly 
resemble  the  aggregations  found  in  the  true  insectivorous  plants. 

Beal  has  described  somewhat  similar  hairs  on  some  thistles. 

It  is  not  the  province  of  this  volume  to  discuss  the  singular 
relationships  which  are  presented  by  these  groups  of  insec- 
tivorous plants.  Attention  must  be  directed,  however,  to  the  fact 
that  Dionsea  and  Drosera,  with  their  widely  different  mechan- 
isms for  the  capture  of  insects,  belong  to  the  same  natural  family  ; 
and  that  Pinguicula  and  Utricularia,  with  methods  equally  di- 
verse, are  venr  nearly  allied  plants.  Such  facts  can  be  explained 
in  part  by  the  theory  presented  in  Volume  I.  page  328,  —  the 
"Theory  of  Descent."1 

1  The  following  list  will  introduce  the  student  to  some  of  the  principal 
works  upon  insectivorous  plants.  As  the  list  is  chronologically  arranged,  it  may 
serve  as  a  brief  history  of  the  subject. 

1768.  John  Ellis  :"  De  Dionaea  muscipula."  A  letter  to  Sir  Charles  Lin- 
naeus descriptive  of  the  method  by  which  this  fly-trap  captures  insects. 

1782.  Roth  :  "  Von  der  Reizbarkeit  des  sogenannten  Sonnenthaues,  Drosera 
rotundifolia  und  longifolia  "  (Beitrage  zur  Botanik,  Bremen,  Th.  1,  no.  iv,  pp. 
60-76).  An  account  of  observations  begun  in  1779  on  the  irritability  of  the 
glands  of  sun-dew  leaves,  showing  that  they  respond  to  contact  with  in- 
sects, but  not  to  a  pin  or  bit  of  straw.  Roth  suggests  that  the  plant  may 
possibly  receive  some  nourishment  from  the  insects.  (In  Darwin's  Botanic 
Garden,  1780,  p.  24,  it  is  stated  that  Whately  had  made  in  England  observa- 
tions similar  to  those  of  Roth. ) 

1791.  Bartram  :  "Travels  through  North  and  South  Carolina,  etc."  This 
book  contains  a  short  sketch  of  the  capture  of  insects  by  Sarracenia. 

1815.  Macbride  :  "  On  the  power  of  Sarracenia  adunca  to  entrap  insects  " 
(Transactions  of  the  Linnaean  Society,  xii.,  1818,  48-52). 

1829.     Burnett,  in  the  Quarterly  Journal  of  Science,  Literature,  and  Arts, 


352  ASSIMILATION. 

921.  Epiphytes,  or  air-plants,  obtain  their  food-materials  wholly 
without  contact  with  the  soil.  It  is  supposed  that  the  ash  materials 

ii.  290,  also  gives  an  account  of  Sarracenia,  together  with  a  description  of  its 
digestive  powers,  and  compares  its  hollow  leaf  to  an  animal  stomach. 

1834.  Curtis,  in  the  Journal  of  the  Boston  Society  of  Natural  History,  i., 
pp.  123-125,  gives  a  description  of  the  irritability  of  Dionaea,  and  of  its  mode  of 
action. 

1848.  Benjamin  :  "  Ueber  den  Bau  und  die  Physiologic  der  Utricularien  " 
(Botanische  Zeitung,  vi.,  pp.  1,  17,  et  seq.). 

1850.     Cohn  :  "Ueber  Aldrovanda  vesiculosa"  (Flora,  p.  673). 

1855.  Greenland  :  "  Note  sur  les  organes  glanduleux  des  Drosera"  (Ann. 
des  Sc.  nat.  bot.,  ser.  4,  tome  Hi.  p.  297). 

1855.  Trecul :  "Organization  des  glandes  pedicellees  de  la  feuille  du 
Drosera  rotundifolia  "  (Ann.  des.  Sc.  nat.  bot.,  ser.  4,  tome  iii.  p.  303). 

1859.  Caspary :    "Aldrovanda    vesiculosa"   (Botanische    Zeitung,    xvii. 
p.  125). 

1860.  Nitschkein  Botanische  Zeitung,  xviii.  p.  57,  and  xix.,  1861,  p.  145, 
gives  an  excellent  description  of  Drosera,  and  an  account  of  simple  but  telling 
experiments  upon  the  sensitiveness  of  the  leaves. 

1860.  Darwin  began  his  experiments  upon  Drosera,  not  published  until 
much  later. 

1862.  Botanische  Zeitung  of  this  year  (p.  185)  contains  a  second  article  on 
the  subject  of  Aldrovanda  by  Caspary. 

1863.  Scott :  "On  the  Propagation  and  Irritability  of  Drosera"  (Garden- 
ers' Chronicle,  p.  30). 

1868.  Canby  published  an  account  of  experiments  on  feeding  Dionsea,  in 
the  Gardener's  Monthly,  p.  229. 

1872.  Ziegler  :  "Sur  un  fait  physiologique  observe   sur  des  feuilles  de 
Drosera"  (Comptes  Rendus,  Ixxiv.  p.  1227). 

1873.  Treat :  "  Observations  on  the  Sun-dew  "  (American  Naturalist,  vii. 
p.  705).     In  this  paper  Mrs.  Treat  describes  experiments  relative  to  feeding 
Drosera  carried  on  in  1871. 

1873.  A.  W.  Bennett :  "On  the  movements  of  the  glands  of  Drosera" 
(British 'Association  Reports,  xliii.  p.  123). 

1873.  Stein  :  "  Ueber  die  Reizbarkeit  der  Blatter  von  Aldrovanda"   (Ver- 
handlungen  des  bot.  Vereins  fiir  die  Prov.  Brandenburg). 

1874.  Burdon  Sanderson  :   "  Venus's  Fly-Trap"  (Nature,  x.  p.  105). 
1874.     Asa  Gray  :   "Insectivorous  Plants"  (Nation,  xviii.  pp.  216,  232). 

An  account  of  the  observations  communicated  by  Darwin,  and  a  short  resume 
of  the  subject  up  to  that  date. 

1874.  Mellichamp  :  "  Researches  on  the  pitchers  of  Sarracenia  variolaris, 
and  the  way  in  which  insects  are  caught  in  them  "  (Nature,  x.  p.  253). 

1874.  Hooker :  Address  before  the  British  Association  for  the  Advance- 
ment of  Science,  published  in  full  in  the  Report  for  1874.     This  address  gives 
an  excellent  account  of  the  digestive  powers  of  various  carnivorous  plants, 
especially  Nepenthes. 

1875.  J.   W.  Clark  :    "On  the  absorption  of  nutrient  material  by  the 
leaves  of  some  insectivorous  plants."     This  article  gives  the  results  of  experi- 
ments on  the  absorptive  capacity  of  Drosera  and  Pinguicula,  conducted  with 
the  aid  of  the  spectroscope. 


EPIPHYTES.  353 

which  they  incorporate  come  to  them  in  the  form  of  dust,  which 
subsequently  dissolves  and  is  absorbed.  The  sources  of  their 
carbon  and  nitrogen  have  already  been  sufficiently  explained. 


1875.  Darwin  :  "  Insectivorous  Plants."  A  work  of  462  pages,  more  than 
half  of  which  is  devoted  to  Drosera.  At  the  close  of  his  exhaustive  discussion 
of  his  experiments  upon  this  plant,  Mr.  Darwin  says :  "I  have  now  given  a 
brief  recapitulation  of  the  chief  points  observed  by  me  with  respect  to  the 
structure,  movements,  constitution,  and  habits  of  Drosera  rotundifolia  ;  and  we 
see  how  little  has  been  made  out  in  comparison  with  what  remains  unexplained 
and  unknown." 

1875.  Reessand  Will  :  "  Einige  Bemerkungen  iiber  fleischessende  Pflan- 
zen  "  (Botanische  Zeitung,  p.  713). 

1875.  Canby  :  "  Darlingtonia  Californica"  (Proceedings  American  Asso- 
ciation, p.  64). 

1875.  Cohn  :    "  Ueber  die   Function   der   Blasen   von  Aldrovanda    und 
Utricularia"  (Beitrage  zur  Biologic  der  Pflanzen). 

1875-6.  Morren  published  in  the  Bulletin  of  the  Royal  Academy  of  Bel- 
gium the  results  of  experiments  which  may  be  interpreted  as  showing  that 
the  plants  derive  no  benefit  from  their  insects. 

1875-6.  Gorup-Besanez  and  Will  published  some  observations  regarding 
a  pepton-forming  ferment  in  plants,  in  Sitzungsberichte  der  physikalisch- 
mediciuisches  Societat  zu  Erlangen. 

1876.  Francis  Darwin  :   "  The  process  of  aggregation  in  the  tentacles  of 
Drosera    rotundifolia"     (Quarterly  Journal   of    Microscopical    Science,    xvi. 
p.  309). 

1876.  Sydney  H.  Vines:  "On  the  digestive  ferment  of  Nepenthes" 
(Journal  of  Anatomy  and  Physiology,  xi.  p.  124). 

1876.  Faivre  :  "Recherches  sur  la  structure,  le  mode  de  formation,  et 
quelques  points  relatifs  aux  fonctions  des  urnes  chez  le  Nepenthes  "  (Comptes 
Rendus,  Ixxxiii.  p.  1155). 

1876.  Munk  :  "  Die  elektrischen  und  Bewegungsercheinungen  am  Blatter 
der  Dionaea  muscipula." 

1877.  Cramer  :  "  TJeber  die  insectenfressenden  Pflanzen." 
1877.     Aschman  :  "  Les  plantes  insectivores,"  Luxemburg. 

1877.  Pfeffer  :  "  Ueber  fleischfressende  Pflanzen  und  iiber  die  Emahrung 
durch  Aufnahme  organischer  Stoffe  iiberhaupt "  (Landwirthsch.  Jahrb.  v. 
Nathusius,  p.  969).  An  excellent  account  of  the  mechanism  and  absorptive 
properties  of  carnivorous  plants. 

1879.  Drude  :  "  Die  insektenfressenden  Pflanzen."  A  full  and  interesting 
examination  of  the  subject  in  Schenk's  Handbuch  der  Botanik. 

1882.  Schimper  :  "  Notizen  iiber  insectenfressenden  Pflanzen  "  (Botanische 
Zeitung,  xl.  p.  225). 

Several  jeux  if  esprit  have  been  published,  in  which  the  remarkable  proper- 
ties of  a  few  humble  plants  have  been  exaggerated  into  accounts  of  man- 
catching  and  man-eating  trees  of  large  size. 


CHAPTER  XI. 

CHANGES   OF  ORGANIC   MATTER   IN   THE   PLANT. 

922.  IT  has  now  been  shown  that  under  the  influence  of  sun- 
light green   plants   produce  organic   matter   out  of  inorganic 
materials.     This  organic  matter  is  conveyed  to  points  where  it 
is  to  be  used,  or  to  temporary  reservoirs  where  it  is  stored  for 
future  use.     It  undergoes  manifold  changes  in  the  plant,  until 
in  the  ordinary  course  of  nature  it  is  resolved  at  last  into  the 
very  materials  from  which  it  originally  came ;  namely,  carbonic 
acid  and  water. 

923.  But  as  the  organic  matter  of  the  plant  represents  in  its 
construction  a  definite  amount  of  energy  of  motion  derived  from 
solar  radiance  transformed  into  the  energy  of  position,  in  its 
apparent  destruction  is  involved  the  reconversion  of  this  energy 
of  position  into  energy  of  motion.     Between  the  first  and  last 
terms  of  these  constructive  and  destructive  processes  very  differ- 
ent periods  of  time  may  elapse  in  different  cases,  according  to 
the  changes  which  the  organic  matter  undergoes. 

924.  That  portion  of  the  organic  matter  which  is  built  into 
the  fabric  of  the  plant  in  the  form  of  cellulose  more  or  less  modi- 
fied is  not  often  broken  down  into  its  original  components  while 
the  organism  is  living ;  but,  by  decay  and  by  combustion,  even 
this  relatively  permanent  substance  is  decomposed,  and  its  ele- 
ments are  finally  given  back  to  the  air  and  soil.     A  certain  por- 
tion of  the   organic   matter,    however,   undergoes   speedy  and 
striking  changes,  and  all   of  these   are   now  to   be   examined 
from  another  point  of  view. 

TRANSMUTATION,   OR  METASTASIS. 

925.  The  physiological  expression  for  the  substance  formed 
by  chlorophyll  in  the  sunlight  is  food.     This  substance  is  util- 
ized by  the  organism  in  many  ways  ;  but  of  these  only  the  fol- 
lowing need  now  be  noticed:   (1)  for  the  supply  of  energy  for 
movements  and  other  work ;  (2)  for  the  repair  of  waste  ;  (3)  for 


TRANSMUTATION.  355 

the  construction  of  new  parts.  The  changes  by  which  these 
processes  are  performed  take  place  in  the  protoplasm  which 
receives  and  in  some  way  disposes  of  the  newly  formed  food. 

926.  Supply  of  energy  for  work.     This  is   furnished   by  the 
process  of  oxidation.     It  will  be  remembered  that  the  inorganic 
materials  concerned  in  the  production  of  the  food  of  the  plant, 
namely,  carbonic  acid  and  water,  are  highly  oxidized  compounds. 
By  assimilation  a  part  of  the  oxygen  is  liberated,  and  the  or- 
ganic matter  formed  is  some  carbohydrate  capable  of  oxidation. 
The  reception  of  oxygen,  the  oxidation  of  the  oxidizable  matter, 
and  the  release  of  the  products  of  oxidation  by  the  plant  are 
collectively  termed  respiration. 

927.  Repair  of  waste.     The  living  matter  of  plants,  like  the 
living  matter  of  animals,  being  the  seat  of  all  the  activities 
manifested  by  the    organism,  is  constantly    undergoing  waste 
and  demanding  repair.     The  repair  of  waste  is  proper  nutri- 
tion. 

928.  The  construction  of  new  parts.    It  has  been  shown  (Chap- 
ter X.)  that  by  the  appropriation  of  nitrogen  by  the  plant  proteids 
are  formed,  and  these  are  in  great  part  utilized  in  the  produc- 
tion of  new  protoplasmic  matter.     So  far  as  the  latter  is  an 
actual  increase  in  substance,  and  not  a  mere  repair  of  waste, 
it  represents  true  growth.     The  growth  of  any  root,  stem,  or 
leaf  consists   in  the  formation  of  new  cells  and  the  increase 
of  these  in  size.     In  this  process  the  production  of  new  cell- 
wall  is  of  course  the  most  conspicuous  phenomenon.     The  per- 
manent increase  in  size  of  the  cell- walls  of  a  plant  disposes  of  a 
large  part  of  the  organic  matter  which  is  prepared  by  assimila- 
tion, and  this  phase  of  growth  is  apt  to  divert  attention  from 
that  which  really  underlies  it ;  namely,  growth  of  the  protoplasm 
itself. 

929.  For  convenience,  the  various  chemical  changes  which 
go  on  within  the  plant  may  be  divided  into  two  groups  ;  namely, 
transmutation  and  complete  oxidation.     In  the  former,  the  or- 
ganic matter  changes  its  properties   in   some   way,    either  by 
the   addition  of  new  materials  or  by  the   reconstruction  of  its 
existing  molecules,  but,  notwithstanding  the  change,  still  re- 
mains organic  matter ;  while  in  the  latter  it  is  resolved  into  its 
original  inorganic  components.    The  change  of  one  kind  of  food 
into  another,  the  transformation  of  starch  into  cellulose,  and  the 
formation  of  proteids,  are  good  examples  of  transmutation :  the 
consumption  of  food  for  the  release  of  energy,  an  example  of 
complete  oxidation.     The  first  of  these  groups  of  changes  cor- 


856      CHANGES   OF  OKGANIC   MATTER  IN  THE  PLANT. 

responds  nearly  to  what  has  been  called  metastasis,1  the  second 
to  respiration.  But  it  must  be  remembered  that  the  distinction 
between  the  two  groups  is  not  absolute. 

930.  The  contrast  between  assimilation  and  respiration  is  very 
marked :   one  is  substantially  the  opposite  of  the  other.     The 
following  tabular  view  displays  the  essential  differences  between 
them. 

Assimilation  proper  Respiration 

Takes  place  only  in  cells  containing  Takes  place  in  all  active  cells. 

chlorophyll. 

Requires  light.  Can  proceed  in  darkness. 

Carbonic  acid  absorbed.oxygen  set  free.  Oxygen  absorbed,  carbonic  acid  set  free. 

Carbohydrates  formed.  Carbohydrates  consumed. 

Energy  of  motion  becomes  energy  of  Energy  of  position  becomes  energy  of 

position.  motion. 

The  plant  gains  in  dry-weight.  The  plant  loses  dry-weight. 

Some  of  the  changes  which  are  grouped  under  transmutation, 
or  metastasis,  present  almost  as  great  a  contrast  to  assimilation 
proper  as  that  shown  in  the  above  table. 

931.  Course  of  transfer  of  assimilated  matters.     In  the  present 
state  of  knowledge  it  is  impossible   to  trace  all   the  chemical 
changes  which  assimilated  matters  undergo  in  the  plant,  or  even 
the  course  which  such  matters  take  ;  only  a  few  of  the  more  ob- 
vious modifications  have  been  investigated.     Before  proceeding 
to  describe  the  important  forms  of  organic  substance  in  the 
plant,  the  following  general  considerations  should  be  presented. 

The  carbohydrates  are  believed  to  be  transferred  from  one 
part  to  another,  in  the  higher  plants,  through  the  thin-walled 
parenchyma.  The  reaction  of  these  cells  is  almost  uniformly 
acid.  The  transfer  takes  place  only  when  the  carbohydrates 
are  in  solution. 

The  albuminoids  are  probably  carried  chiefly  by  means  of 
the  soft  bast  of  the  fibro- vascular  bundles  ;  the  cells  of  this  bast 
have  a  slightly  alkaline  reaction. 

But  that  these  are  not  the  only  paths  of  transfer,  appears  from 
the  frequent  occurrence  of  minute  starch-grains  in  the  sieve- 
cells,  and,  on  the  other  hand,  of  dissolved  albuminoids  in  paren- 
chyma cells. 


1  The  German  word  Stoffwechsel  is  usually  translated  metastasis,  — a  word 
long  known  in  medicine  with  a  totally  different  signification  from  that  above. 
Schwann's  term,  metabolism,  much  used  in  human  physiology,  expresses  its 
idea  better,  but  for  some  reasons  the  term  transmutation  appears  preferable. 


CARBOHYDRATES.  357 

The  direction  of  transfer  of  the  above  compounds  is  towards 
the  point  of  use,  or  of  storing ;  there  is  never  any  approach  to  a 
true  circulation  throughout  the  plant,  corresponding,  as  was  for- 
merly taught,  to  the  circulation  in  animals. 

932.  Classification  of  the  principal  organic  products.    For  the 
present  purpose  these   may  be  conveniently  grouped  into   (1) 
those  which  are  free  from  nitrogen,  and  (2)   those  which  con- 
tain nitrogen.     Some   have  been  already  treated  of   in  earlier 
pages   of  this  volume ;  of  the   rest,  little   more   than   a   mere 
enumeration  can  here  be  given. 

933.  Products  free  from  nitrogen.    I.  Carbohydrates.   In  general 
these  are  solid  bodies  many  of  which  are  soluble  in  water.    They 
are  conveniently  divided   into  the  cellulose  group,  having   the 
empirical  formula,  CGH10O5,  and  the  sugars,  —  grape-sugar,  fruit- 
sugar,  and  cane-sugar. 

THE  CELLULOSE  GROUP  comprises  the  following  isomeric 
bodies :  — 

934.  Cellulose.     This  substance  (see  page  31)  is  regarded  as  a 
product  of  the  direct  transformation  of  starch  or  its  equivalent. 
When  once  separated  from  the  protoplasm  as  cell- wall,  cellulose 
is  not  again  dissolved  save  in  the  exceptional  cases  of  germi- 
nation where  it  serves  as  a  food.      Sachs   has  shown  that  in 
the  germination  of  the  date,  the  pitted  thickening  masses  of  the 
cell-walls  of  the  endosperm  are  dissolved  and  utilized  by  the 
embryo. 

935.  Starch  (see  pages  47-50).    The  occurrence  of  this  sub- 
stance in  the  chlorophyll  granules  under  certain  conditions  has 
already  been  described.     Its  occurrence  in  reservoirs  of  food, 
and  the  relation  of  this  to  the  starch-generators,  have  been  dis- 
cussed in  174. 

The  following  table  gives  some  idea  of  the  amount  of  starch 
found  in  the  ordinary  commercial  sources :  — 

Source.  Amount  of  starch  present. 

Grains  of  wheat 64      per  .cent. 

Grains  of  corn 65        "      " 

Grains  of  rice 76        "      " 

Potato  tubers 15-29  "      " 

When  starch  is  to  be  transferred  from  the  places  where  it  is 
held  in  reserve  to  the  points  where  it  is  to  be  consumed,  it  is 
converted  into  a  form  of  sugar  by  some  one  or  more  of  the 
unorganized  ferments  occurring  in  plants.  Although  the  sugar 
thus  formed  passes  at  once  into  solution,  it  is  a  curious  fact 


358      CHANGES   OF   ORGANIC   MATTER   IN   THE   PLANT. 

that  at  certain  points  during  its  course  this  solution  may  tran- 
siently exhibit  more  or  less  fine-grained  starch.  The  tendency 
of  starch  to  form  in  this  way  is  very  remarkable  in  the  process 
of  germination. 

936.  Inulin.    This  substance  is  dissolved  in  cell-sap  (see  183), 
but  is  easily  separated  from  it  upon  immersion  of  the  plant  sec- 
tions in  alcohol.    It  replaces  starch  in  the  roots  and  root-like 
stems  of  many  perennials  belonging  to  the  following  orders,  — 
Liguliflorse  (Composite),  Campanulaceae,  and  Lobeliaceae. 

937.  Lichenin  is  abundant  in  certain  lichens,  amounting  in 
Cetraria  Islandica  to  more  than  40  per  cent. 

938.  Dextrin.     Under  this  name  are  comprised  at  least  two 
substances1  which  are  produced  during  the  transformation  of 
starch  into  sugar.      Dextrin   occurs   in   the   young  sprouts  of 
potato,  in  most  bulbs  as  they  are  starting,  and  in  the  spring  sap 
of  many  trees. 

939.  The  Gums.     These   are   amorphous   substances   which 
either  dissolve  in  water  or  merely  swell  in  it  to  form  soft  masses 
or  thick  viscous  liquids.     An  example  is 

Arabin  (2C6H10O.-(-H2O),  the  chief  constituent  of  Gum  Arabic, 
obtained  from  a  species  of  Acacia.  It  is  found  associated  with 
arabic  acid,  which  is  supposed  to  be  combined  with  calcium.  It 
occurs  in  cherry-tree  gum,  and  to  a  slight  amount  in  the  gum  of 
many  other  plants. 

Of  those  gums  which  do  not  truly  dissolve,  must  be  mentioned 
Cerasin,  abounding  in  cherry-tree  gum ;  Bassorin,  or  the  essen- 
tial constituent  of  gum-tragacanth  ;  and  Vegetable  Mucus,  which 
occurs  in  the  seed-coats  of  flax,  the  pseudo-bulbs  of  many  or- 
chids, and  the  leaves  of  some  mallows. 

940.  The  Pectin  ^Bodies.      According  to  Fremy  these  are 
derivatives  from  pectose,  a  neutral  insoluble   substance  found 
in  unripe  fruits  and  in  some  fleshy  roots.     Pectose  undergoes 
various  changes  not  yet  understood.     Vegetable  jelly,  obtained 
by  boiling  subacid  fruits,  is  a  familiar  example  of  one  of  the 
products  of  such  changes. 

941.  THE  SUGAR  GROUP.     The  more  common  members  of  this 
group  are  grape-sugar,  fruit-sugar,  and  cane-sugar.     The  em- 
pirical formulas  of  these  substances  have  simple  relations,  ex- 
hibited in  the  following  table,  in  which  the}'  are  compared  with 
that  of  starch  :  — 

1  For  an  account  of  the  allied  substances,  amylodextrin  and  achroodextrin, 
see.  W.  Nageli,  Beitrage  zur  naheren  Kenntniss  der  Starkegruppe,  1874. 


THE  SUGARS. 

Starch,  C6H1005 

Cane-sugar,  C12H22OU 

Grape-sugar  and  fruit-sugar,  C6H12O6 
Thus, 


Starch.  Water.         Cane-sugar. 


u  +  H20  =  C6H1206  +  C6H1206 

Cane-sugar.      Water.       Grape-sugar.      Fruit-sugar. 

The  three  following  classes  of  sugars,  based  upon  their  rela- 
tions to  fermentation,  have  been  made  :  (1)  directly  fermenta- 
ble, (2)  indirectly  fermentable,  (3)  non  -fermentable  sugars.  To 
the  third  class  belong  Arabinose,  Sorbit,  etc.,  which  need  no 
further  notice  here. 

The  directly  fermentable  sugars  are  grape-sugar,  fruit-sugar, 
and  inverted  sugar. 

942.  Grrape-sugar,  otherwise  termed  glucose  (or,  on  account 
of  its  turning  the  plane  of  polarization  to  the  right,  dextrose),  is, 
as  its  name  indicates,  abundant  in  the  grape,  where  it  may  form 
from  10  to  30  per  cent  of  the  juice.     Figs  contain,  on  an  aver- 
age, 12  per  cent  ;  sweet  cherries,  9  to  10  per  cent  ;  apples  and 
pears,  7  to  10  per  cent  ;  plums,  2  to  5  per  cent  ;  and  peaches 
less  than  2  per  cent  of  this  sugar. 

943.  Fruit-sugar,  sometimes  known  as  laevulose,  is  uncrys- 
tallizable.     It  is  associated  in  most  ripe  fruits  with  dextrose. 

944.  Inverted  sugar  occurs  in  some   ripe   fruits,  where,  as 
Buignet  has  shown,  it  is  formed  from  cane-sugar  by  the  action 
of  a  ferment  and  not  of  a  fruit-acid.     It  is  also  found  in  the 
so-called  honey-dew  of  the  leaves  of  the  Linden.1 

945.  The   indirectly  fermentable  sugars,  of  which  common 
cane-sugar  may  be  taken  as  the  best  example,  ferment  under  the 
influence  of  yeast  only  when  the}'  have  first  undergone  a  change 
by  which  they  are  converted  into  other  sugars. 

946.  Cane-sugar  occurs  in  the  cell-sap  of  many  plants,  often 
in  large  amount.     The  following  percentages  are  regarded  as 
average  ones  :  — 


1  According  to  Boussingault,  120  square  metres  of  linden  leaves  yield  in 
a  single  warm  July  day  between  two  and  three  kilograms  of  honey-dew.  As 
to  whether  this  substance  is  a  product  of  an  insect,  or  an  exudation  from  leaves 
under  peculiar  conditions,  is  not  yet  settled  (Ebermayer  :  Chemie  der  Pflanzen, 
1882,  p.  255). 


360      CHANGES   OF   ORGANIC   MATTER   IN   THE   PLANT. 

Sugar-cane  stem 16-18  per  cent. 

Sugar-beet 10-14        " 

Sorghum 10-11        " 

Indian  corn 6-7        " 

Sugar  maple 8        " 

947.  Products  free  from  nitrogen,     n.  Vegetable  acids.     Of 

these  the  most  widely  distributed  are  oxalic,  tartaric,  citric,  and 
malic  acids. 

948.  Oxalic  acid  (C2H204)  occurs  in  almost  every  plant,  the 
amount  in  some  reaching  as  high  as  4  per  cent.     Most  of  it  is 
combined  with  calcium  or  with  potassium,  a  part  remaining  un- 
combined.     According  to  Miiller,1  the  fresh  leaves  of  sugar-beet 
contain  4  per  cent  of  this  acid,  of  which  one  third  is  in  solution. 

949.  Tartaric  acid  (C4H6O6)  occurs  free,  and  also  combined 
with  potassium  in  the  juice  of  the  grape  and  many  other  fruits. 

950.  Citric  acid  (C6H8O7)  occurs  in  the  amount  of  6  to  9 
per  cent  in  the  juice  of  lemons  and  allied  fruits,  and  is  asso- 
ciated with  other  acids  iu  most  of  our  subacid  fruits,  such  as 
currants,  cherries,  etc. 

951.  Malic  acid  (C4H606)  occurs  free,  or  combined  with  cal- 
cium, in  the  juices  of  many  fruits  and  in  the  sap  of  many  plants. 
It  imparts  the  sour  taste  to  our  most  common  fruits. 

952.  Products  free  from  nitrogen.     III.  Fats,  or   Glycerides. 
According  to  Ebermayer  most  of  the  fats  which  occur  in  plants 
are  mixtures  (not  compounds)  of  the  following  three  kinds  of 
fats  in  different  proportions :  Tristearin  or  stearin,  tripalmatin 
or  palmatin,  triolein  or  olein.    The  oils  in  most  seeds,  however, 
are  free,  fatty  acids ;  namely,  stearic,  palmitic,  and  oleic. 

The  fats  are  regarded  as  compound  ethers  formed  from  the 
triatomic  alcohol  glycerin,  whence  they  have  been  sometimes 
termed  Glycerin  ethers.  The  following  formulas  exhibit  one  view 
as  to  their  constitution :  — 

Tristearin ( 

Tripalmatin 

Triolein     ...  ^18^/8  I  o8 


Stearic  acid 

Palmitic  acid 

Oleic  acid 

(Glycerin C8H6(OH)8) 

1  Quoted  by  Ebermayer,  Chemie  der  Pflauzen,  p.  320. 


TANNIN  AND  ALLIED  SUBSTANCES.  861 

The  oils  form  very  intimate  mixtures  with  the  albuminoids  in 
many  cases,  especially  in  seeds  of  such  plants  as  Ricinus,  etc. 
According  to  Sachs,  "  in  the  germination  of  all  oily  seeds,  sugar 
and  starch  are  produced  in  the  parenchyma  of  every  growing 
part,  disappearing  from  them  only  when  the  growth  of  the  masses 
of  tissue  concerned  has  been  completed.  Since,  in  the  case  of 
Ricinus,  the  endosperm  grows  also  independently,  starch  and 
sugar  are,  in  accordance  with  the  general  rule,  temporarily  pro- 
duced in  it.  The  cotyledons  apparently  absorb  the  oil  as  such 
out  of  the  endosperm,  whence  it  is  distributed  into  the  paren- 
chyma of  the  hypocotyledonary  stem  and  of  the  root,  serving 
in  the  growing  tissues  as  material  for  the  formation  of  starch  and 
sugar,  which  on  their  part  are  only  precursors  in  the  production 
of  cellulose.  In  these  processes  tannin  is  also  formed,  which  is 
of  no  further  use,  but  remains  in  isolated  cells,  where  it  collects 
apparently  unchanged  until  germination  is  completed.  It  can 
scarcely  be  doubted  that  the  material  for  the  formation  of  this 
tannin  is  also  derived  from  the  endosperm,  although  perhaps  only 
after  a  series  of  metamorphoses.  The  absorption  of  oxygen, 
which  is  an  essential  accompaniment  of  ever}^  process  of  growth 
and  especially  of  germination,  has  in  this  case,  as  in  that  of  all 
oily  seeds,  an  additional  significance,  inasmuch  as  the  formation 
of  carbohydrates  at  the  expense  of  the  oil  involves  the  appro- 
priation of  oxygen."  1 

Vegetable  wax  is  closely  allied  to  the  fats. 

953.  Products  free  from  nitrogen.  IV.  Certain  astringents. 
This  indefinite  group  comprises  various  matters  differing  slightly 
from  one  another  in  some  particulars,  but  agreeing  in  possessing 
a  faint  acid  character,  in  changing  color  with  salts  of  iron,  and 
in  combining  with  certain  protein  matters.  Tannin  is  sometimes 
placed  in  the  next  category,  namely,  among  the  glucosides  ;  but 
according  to  Schiff  it  is  digallic  acid.  The  most  important  mem- 
bers of  this  group  are  Tannin  (the  so-called  tannic  acid),  Gallic 
acid,  and  the  astringent  principle  in  Cinchona,  Catechu,  and 
Kino.  According  to  Nageli,  these  matters  are  to  be  found  in 
buds,  in  unripe  fruits,  and  in  those  petals  which  become  red  or 
blue,  dissolved  in  the  cell-sap  and  diffusing  through  cell-walls. 
Tannin  sometimes  exists  in  little  globules  of  solution,  enveloped 
by  a  delicate  film  of  albuminous  matter ;  for  example,  in  the  cells 
of  the  pulvinus  of  Mimosa  and  in  the  bark  of  many  ligneous 
plants  (Birch,  Poplar,  etc.).  The  following  views  are  held  as  to 

1  Text-book,  2d  English  ed.,  p.  716. 


362      CHANGES   OF   ORGANIC   MATTER   IN   THE   PLANT. 

the  formation  of  this  substance :  Many  authors  regard  it  as  a 
product  of  the  retrograde  metamorphosis  of  certain  carbohy- 
drates ;  Sachsse  thinks  that  it  always  attends  the  formation 
of  cellulose  from  starch,  and  that  there  is  a  slight  evolution 
of  carbonic  acid ;  Wiesner  regards  it  as  intermediate  in  the 
series  which  begins  with  the  carbohydrates  and  ends  with  the 
resins.  This  last  view  is  also  held  by  Hlasiwetz,  who  has  ob- 
tained the  same  products  from  tannin  as  from  the  resins,  when 
each  was  fused  with  potassic  hydrate. 

It  is  a  significant  fact  that  all  the  barks  which  are  rich  in  tannin 
are  also  rich  in  starch. 

Nothing  is  positively  known  as  to  the  function  of  tannin  and 
its  associated  bodies  in  the  plant.  By  Hartig  the}*  have  been 
looked  upon  as  reserve  materials ;  but  Schroeder  was  not  able 
to  verify  Hartig's  observations.  By  most  observers  these  sub- 
stances are  regarded  as  waste  products,  having  no  further  nutri- 
tive function,  but  possibly  playing  some  part  in  the  formation  of 
colors.  The  following  table  l  shows  their  amount  in  some  of  the 
barks  and  other  parts  used  in  tanning :  — 

Galls 30-77  per  cent. 

Catechu 40-50 

Divi-Divi 30-40 

Sumach 12-18 

Oak  bark 7-20 

Willow  bark 8-12 

Hemlock  bark 13-16 

954.  Products  free  from  nitrogen.    V.  Most  Glucosides.    These 
are  substances  which  under  certain  conditions,  especially  by  the 
action  of  unorganized  ferments,  are  broken  up  into  glucose  or 
some  allied  sugar,  and  at  the  same  time  some  other  body  capable 
of  further  decomposition.     Most  of  them  are  soluble  in  water. 
The  following  are  among  some  of  the  best  known  :  salicin,  coni- 
ferin,  sesculin,  quercitrin.     Tannin  is  often  placed  among  the 
Glucosides. 

955.  Products  free  from  nitrogen.     VI.  Ethereal  oils.     These 
are  volatile  liquids  generally  approaching  Terpene  (C10H]6)   in 
chemical  composition.     Nothing  is  certainly  known  as  to  their 
formation  in  the  plant.     They  are  not  again  taken  up  as  plastic 
matter,  but  simply  serve  some  function,  often  that  of  attraction 

1  For  other  determinations  see  Ebermayer's  Chemie  der  Pflanzen,  p.  452, 
from  which  most  of  the  above  are  taken  ;  also  see  the  excellent  table  in  the 
Tenth  Census,  vol.  ix.,  p.  265. 


ALBUMIN-LIKE  MATTERS.  863 

or  of  protection.  To  their  presence  is  due  the  fragrance  of  many 
fruits  and  flowers,  notably  those  of  orange,  bergainot,  and  the 
mints.  Associated  with  the  ethereal  oils,  the  camphors  occupy  a 
prominent  place.  They  are  generally  regarded  as  the  products 
of  the  slight  oxidation  of  some  ethereal  oils,  The  following  is 
the  best  known,  C10H16O  (Laurel-camphor). 

956.  Products  free  from  nitrogen.     VII.    Resins  and  Balsams. 
These  substances,  which  differ  much  in  consistence,  color,  and 
other  physical  properties,  contain  comparatively  little  oxygen, 
are  mostly  amorphous,  insoluble  in  water,  and  sometimes  pos- 
sess a  slight  acid  reaction. 

Balsams  are  defined  as  "  mixtures  of  resins  with  volatile  oils, 
the  resins  being  produced  from  the  oils  by  oxidation,  so  that  a 
balsam  ma}7  be  regarded  as  an  intermediate  product  between 
a  volatile  oil  and  a  perfect  resin."  l 

The  Balsams  are  generally  divided  into  two  groups :  (1)  those 
containing  much  cinnamic  acid,  as  Balsam  of  Tolu,  Peru,  etc. ; 
and  (2)  those  which  are  purely  oleo-resinous,  as  Balsam  Copaiba, 
Fir,  etc.2 

Certain  resins  and  caoutchouc-like  matters  are  found  in  large 
amount  in  the  latex. 

957.  Products  containing  nitrogen.     I.  The  albumin-like  mat- 
ters.    Ritthausen  classifies  these  substances  into  (1)  Albumin  of 
plants  ;  (2)  Casein  of  plants  ;  (3)  Gelatin  of  plants. 

Albumin  of  plants  is  the  term  applied  to  the  protein  mat- 
ters which  readily  coagulate  from  their  aqueous  solutions  upon 
the  action  of  heat  or  acids.  The  coagula  dissolve  more  or  less 
readily  in  potassic  hydrate,  exhibiting  considerable  differences 
in  respect  to  solubility.  They  contain  from  2.6  to  4.6  per  cent 
of  ash,  and  have  the  following  elementary  composition :  — 

Carbon 52.31-54.33  per  cent. 

Hydrogen 7.13-  7.73       " 

Nitrogen 15.49-17.60       " 

Sulphur 76-  1.55       " 

Oxygen 20.55-22.98       " 

Casein  of  plants  comprises  the  following  substances :  legu- 
min,  gluten-casein,  conglutin.  Solutions  of  these  are  precipi- 
tated by  dilute  acids  and  by  rennet.  The  precipitates  are  readily 

1  Watts :  Dictionary  of  Chemistry,  i.,  1863,  p.  491. 

2  A  solution  of  the  coloring-matter  of  alkanet  root  in  dilute  alcohol  applied 
to  a  thin  section  of  a  plant  containing  resins  colors  the  resins  red  after  a  few 
minutes,  but  does  not  serve  to  distinguish  one  from  another. 


S64     CHANGES  OF  OftGANlC  MATTER  IN  THE  PLANT. 

soluble  in  a  solution  of  basic  potassic  phosphate.  Their  ultimate 
composition  is  nearly  the  same  as  that  of  the  group  just  men- 
tioned. 

Gelatin  of  plants.  The  associated  matters  are  (1)  Gliadin, 
(2)  Mucedin,  (3)  Gluten-fibrin.  These  bodies  are  soluble  in 
alcohol,  and  in  water  containing  a  small  amount  of  acid  or 
alkali.  In  their  fresh  state  they  are  tough,  viscid  masses,  only 
slightly  soluble  in  water.1 

958.  Weyl  does  not  accept  Ritthausen's  classification,  but 
holds  that  legumin  is  a  mixture  of  vegetable  vitellin  and  casein ; 
and  further,  that  there  is  no  true  casein  in  seeds,  —  the  sub- 
stance called  by  this  name  being  a  product  of  secondary  changes 
in  the  laboratory. 

959.  Products  containing  nitrogen.    II.  Asparagin  (C4H8N2O3). 
This  substance  occurs  in  the  shoots  of  Asparagus  officinalis  and 
many  other  plants,  from  which  it  can  be  obtained  in  the  form  of 
transparent  crystals  of  the  orthorhombic  system.     It  is  merely 
necessary  to  evaporate  the  juice  of  the  plants  to  the  consist- 
ence of  a  thin  syrup,  and  after  allowing  it  to  stand  for  a  time 
the  crystals  will  separate,  and  may  be  purified  by  recrystalliza- 
tion.     Pfefler  describes  the  following  useful  method  of  preparing 
them  upon  the  slide  of  the  microscope :  A  moderately  thick  sec- 
tion of  the  tissue  suspected  of  containing  asparagin  is  placed  on 
a  slide,  covered  with  a  bit  of  glass,  and  treated  with  absolute 
alcohol,  when  the  crystals  will  be  thrown  down  in  the  cells,  or 
will  form  in  the  alcohol  outside  of  the  specimen.     The  character 
of  the  crystals  can  be  known  certainly  by  their  insolubilit}'  in  a 
concentrated  aqueous  solution  of  the  same  substance  (see  46). 

The  amount  of  asparagin  in  certain  plants  has  been  given  as 
follows :  — 

Name  of  Plant.  Per  cent  of  Asparagin.  Observer. 

Roots  of  Althaea    ....        2.      ...  Plisson  and  Henry. 

Vetch  germs 1.5    ...  Piria. 

Radicles  of  a  germinating 
plant  dried  at  100  C.   .     .       10.5    .     .     .  Beyer. 

960.  Asparagin  possesses  its  chief  interest  from  the  part 
which  it  probably  plays  in  the  transfer  of  nitrogenous  matters 
through  the  plant.     According  to  Pfeffer,  although  it  cannot  be 
detected  with  certainty  in  the  seeds  of  the  vetch  and  pea,  it 
appears  in  the  young  parts,  especially  in  the  lines  of  transfer  (for 


1  Hunt  has  called  attention  to  a  curious  relation  between  the  composition 
of  animal  gelatin  and  that  of  starch  to  which  ammonia  is  added. 


ASPARAGIN. 


365 


example,  the  petioles  of  the  cotyledons).  That  the  source  of  the 
asparagin  must  be  the  reserve  albuminous  matters  in  the  seed, 
appears  from  the  following  consideration  :  "  The  absolute  amount 
of  nitrogen  remains  the  same  during  germination,  and  the 
nitrogen  of  seeds  is  all  or  nearly  all  contained  in  their  albumi- 
nous ingredients."  *  Asparagin  and  the  chief  proteid  of  the 
seeds  in  leguminous  plants  have  been  thus  compared :  — 


Asparagin. 

Legumin. 

Difference 

Carbon  

36.4 

64.9 

+28.5 

6  1 

8  8 

•4-2  7 

21.2 

21.2 

0.0 

Oxygen  . 

36.4 

30.6 

—5.8 

"Asparagin  contains  less  carbon  and  hydrogen  but  more 
oxygen  than  legumin  and  other  proteids.  Consequently  if  the 
whole  of  the  nitrogen  of  legumin  is  used  in  the  formation  of 
asparagin,  a  considerable  quantity  of  carbon  and  l^drogen  must 
be  given  off  and  a  certain  amount  of  oxygen  absorbed.  Exactly 
the  opposite  will  take  place  upon  the  conversion  of  asparagin 
into  proteid."  l 

961.  Products  containing  nitrogen.    HI.  The  alkaloids.    These 
substances  all  possess  the  power  of  uniting  with  acids  to  form 
salts,  and  they  are  often  described  as  basic  alkaloids.     Among 
the  most  important  are  Morphia,  Quinia,  and  Strychnia. 

The  number  of  alkaloids  now  known  is  very  great,  and  the 
modes  in  which  they  are  found  combined  in  the  plant  are  very 
diverse.  They  are  more  abundant  in  those  plants  which  are 
grown  under  conditions  of  considerable  warmth,  and  are  much 
more  abundant  in  some  parts  of  the  plant  than  in  others,  as  is 
shown  by  the  case  of  morphia.  Nothing  is  positively  known  as 
to  their  origin  or  proper  function  in  the  organism.  It  should 
be  mentioned,  however,  that  many  of  them  when  applied  to 
the  very  plants  from  which  they  were  prepared  prove  to  be 
poisonous  ;  thus,  morphia  poisons  the  poppy. 

962.  Products  containing  nitrogen.     IT.  Unorganized  ferments. 
It  has  long  been  known  that  there  must  exist  in  certain  parts  of 


1  Pfeffer,  in  Sachs's  Text-Book,  1882,  p.  719.  For  a  full  account  by  Pfeffer, 
see  Pringsheim's  Jahrbiicher,  viii.,  1872,  p.  429  ;  and  Monatsbericht  der  Ber- 
lin Akademie,  1873,  p.  780.  See  also  Husemaun  and  Hilger :  Die  Pflanzen- 
stoffe,  i.,  1882,  p.  264. 


866     CHANGES  OF  ORGANIC  MATTER  IN  THti  PLAN*. 

plants,  notably  in  seeds,  compounds  which  possess  the  power  of 
effecting  changes  in  the  character  of  starch,  etc.  ;  but  it  was  not 
until  1873  that  a  method  was  given  which  enables  us  to  isolate 
these  compounds  in  a  state  of  comparative  purity.  This  method 
is  based  upon  their  solubility  in  glycerin,  and  their  ready  pre- 
cipitation from  glycerin  solutions  by  means  of  common  alcohol.1 
By  the  use  of  this  method  Gorup-Besanez  has  been  able  to 
obtain  from  the  seeds  of  vetch,  flax,  etc.,  a  ferment  which  is 
soluble  in  water  and  glycerin.  The  substance  contains  7.76  per 
cent  of  ash  constituents  and  4.5  per  cent  of  nitrogen.  Its  solu- 
tions convert  starch  into  sugar  very  rapidly  at  the  temperature  of 
20°-30°  C. ;  and  in  the  presence  of  a  dilute  acid,  for  instance 
hydrochloric,  it  has  the  power  of  peptonizing  proteids.  In  solu- 
tion, it  loses  its  activity  at  80°  C.  ;  but  if  carefully  dried,  it  can 
stand  a  temperature  of  120°  C.  Up  to  the  present  time  no  fer- 
ment capable  of  effecting  changes  in  the  fats  of  plants  has  been 
isolated.2 

963.  Baranetzky  has  shown  that  in  the  conversion  of  starch 
into  sugar  there  are  two  phases :  (1)  the  formation  of  dextrin, 
and  (2),  at  a  somewhat  higher  temperature,  the  formation  of 
sugar.     He  observed  an  acid  reaction  in  the  ferment. 

964.  In  the  sap  of  Carica  papaya,  Wurtz  and  Bouchut 8  have 
isolated  a  peptonizing  ferment  which  acts  promptly  upon  albu- 
minoids.    The  juices  of  several  tropical  fruits  are  said  to  have 
the  property  of  softening  meats,  and  this  action  is  regarded  as 
dependent  upon  some  unorganized  ferment. 

965.  Besides  the  products  already  enumerated,  there  are  some 
bitter  and  extractive  matters  and  some  coloring  substances  which 
do  not  naturally  fall  into  any  of  the  groups  described. 

966.  From  the  facts  which  have  now  been  presented,  it  is 
clear  that  the  composition  of  the  sap  which  escapes  from  a  plant 
when  it  is  wounded  must  be  very  complex.     The  juices  of  a 
plant  contain  all  its  dissolved  mineral  matters,  gases  in  solution, 
and  numerous  members  of  both  of  the  nitrogenous  and  non- 
nitrogenous  groups  already  mentioned. 

1  Hufner.  Journal  fur  praktische  Chemie,  v.,  1872,  p.  372,  and  xi.,  1875, 
p.  43. 

*  For  a  short  account  of  the  work  of  Kosmann  (Journal  de  Pharmacie  et  de 
Chimie,  ser.  4,  tome  xxii.  p.  335)  and  that  of  Krauch  (Versuchs-Stationen, 
xxiii.  p.  77),  see  Husemann  and  Hilger  :  Die  Pflanzenstoffe,  I,  1882,  p.  238. 

»  Comptes  Rendus,  Ixxxix.,  1879,  p.  425  ;  xci.,  1880,  p.  787.  See  also  the 
following  :  Duclaux  :  Comptes  Rendus,  xci.  p.  731,  and  Hansen  :  Sitz.  der 
physikmedicin.  Societat  zu  Erlangen,  1880. 


RESPIRATION.  367 


RESPIRATION. 

967.  It  has  been  long  known  that  air  is   necessary  for  the 
germination  of  seeds.1    In  1777  Scheele 2  pointed  out  that  in  this 
process,  as  in  the  breathing  of  animals,  oxygen  (called  by  him 
fire  air)  is  consumed  and  carbonic  acid  (called  by  him  air-acid) 
is  given  off.      Two  years  later,  Ingenhousz  8  showed  that  all 
plants  at  night  give  off  fixed  air  (carbonic  acid),  and  in  1804 
Saussure  proved  that  all  plants  require  oxygen  for  their  growth. 
In  1838  Meyen4  clearly  defined  the  scope  of  respiration  in  plants, 
since  which  time  it  has  been  carefully  examined  in  most  of  its 
relations. 

968.  The  relations  of  gases  to  plants,  so  far  as  their  absorp- 
tion and  elimination  are  concerned,  have  been  sufficiently  dis- 
cussed in  Chapter  X.     It  is  merely  necessary  to  state  at  present 
that  oxygen  is  readily  absorbed  by  all  parts  of  plants,  and  that 
the  intercellular  passages  (519)  form  a  means  by  which  it  can 
traverse  the  whole  plant  very  rapidly. 

969.  In  its  simplest  phases  respiration  consists  in  the  absorp- 
tion of  oxygen,  the  oxidation  of  oxidizable  organic  matters,  and 
the  evolution  of  the  products 

of  oxidation;  namely,  carbonic 
acid  and  water.  Some  other 
products  are  often  formed  in 
minute  amount,  but  these  may 
be  here  disregarded. 

970.  Measurement   of   Res- 
piration.    Respiration  can  be 
measured  very  nearly  by  the 
amount  of  oxygen  which  dis- 
appears or  by  the  amount  of 
carbonic  acid  which  is  given 
off.     The  ordinary  apparatus 
for  examining  respiration   is 
based  upon  the  measurement 
of  the  latter,  and  consists  es- 
sentially of  some  application  of  potash-bulbs,  or  wash-bottles  (see 
Fig.  163),  for  the  interception  of  all  evolved  carbonic  acid.     The 


1  See  Malpighi :  Opera  omnia,  1686. 

2  Chemische  Abhandlung  von  der  Luft,  1777. 

8  Experiments  upon  Vegetables,  1779,  p.  xxxvi. 
«  Pflanzenphysiologie,  ii.,  1838,  p.  1C2. 


368      CHANGES   OP  ORGANIC   MATTER   IN   THE  PLANT. 

air  supplied  to  the  seeds  in  the  bell-jar,  of  course  first  carefully 
freed  from  every  trace  of  carbonic  acid,  is  drawn  through  b}- 
means  of  an  aspirator,  and  in  the  bulbs  all  the  carbonic  acid 
derived  from  the  germinating  seeds  is  retained. 

971.  Plants  in  dwelling-houses.     To  what  extent  can  house- 
plants  injure  the  air  of  rooms  at  night?    The  carbonic  acid  which 
is  given  off  by  plants  comes  from  the  breaking  up  of  assimilated 
matters  in  the  various  activities  of  the  organism,  such  as  growth, 
movements,  etc.     But  the  total  amount  of  work  done  by  any 
plant  under  the  conditions  to  which  ordinary  house-plants  are 
subjected  is  represented  by  the  oxidation  of  a  very  small  amount 
of  food.     From  the  most  trustworthy  data  it  is  safe  to  say  that 
in   the  case  of   one   hundred  average   house-plants  the  whole 
amount  of  carbonic  acid  resulting  from  such  oxidation  .during 
work  would  not  vitiate  the  atmosphere  of  a  moderate-sized  room 
to  any  appreciable  extent ;  in  fact,  would  be  exceeded  by  the 
amount  evolved  from  a  common  candle  burning  for  the  same 
length  of  time. 

972.  Relation  of  the  carbonic  acid  given  off  to  the  oxygen 
absorbed.      Owing  to  the  fact  that  part   of  the  carbonic  acid 
produced   during   respiration  is  retained  within  the  plant,  and 
that  water  is  formed  as  a  product  of  respiration,  it  is  difficult  to 
determine  the  exact  relations  of  volume  of  the  absorbed  oxygen 
and  the  evolved  carbonic  acid.     It  is  known,  however,  that  in 
certain  cases  the  amount  of  carbonic  acid  evolved  is  less  than 
would  be  expected  from  the  amount  of  ox3Tgen  absorbed.     This 
is  well  shown  when  the  germination  of  oily  seeds  is  compared 
with  that  of  seeds  containing  chiefly  starch.     When  oily  seeds 
germinate,  the  amount  of  carbonic  acid  is  appreciably  less  than 
that  given  off  by  starchy  seeds.     Hellriegel  has  shown  that  in 
one  instance  the  fixation  of  oxj'gen  amounted  to  an  increase  in 
weight  of  1.15  percent. 

973.  The  free  oxygen  of  the  atmosphere  is  ample  for  the  respi- 
ratory process.     Saussure1  has  shown  that  the  amount  in  the 
atmosphere  can  even  be  reduced  one  half  without  materially 
interfering  with  the  functions  of  the  plant. 

Most  observers  have  found  that  in  pure  oxygen  there  is  an 
increase  in  the  activity  of  the  respiratory  function. 

Bert2  has  conducted  interesting  experiments  upon  the  effect 

1  Quoted  by  Pfcffer,  Pflanzenphysiologie,  i.  p.  373. 

3  For  a  discussion  of  this  question,  particularly  with  reference  to  the  lower 
organisms,  consult  Bert :  La  pression  barometrique,  1878. 


PERIODS   OF   REST.  369 

of  pressure  on  the  various  functions,  by  which  it  appears  that  in 
ordinary  air,  under  a  pressure  of  six  atmospheres,  Mimosa  per- 
ished quickly.  In  an  atmosphere  under  high  compression  seeds 
germinated,  if  at  all,  very  slowly. 

974.  Influence  of  temperature  upon  respiration.      Respiration 
can  go  on  at  low  temperatures,  even  near  the  freezing-point  of 
water.     The  rate  of  respiration  increases  with  rise  of  tempera- 
ture, as  will  be  seen  from  the  following  figures  for  germinating 
beans :  — 1 

„,„_ ,  Amount  of  carbonic  acid 

Temperature.  giyeu  off  each  hour 

2°C 10.56  mgr. 

6° 21.22  " 

18° 32.34  " 

20° 39.60  " 

30° 47.52  " 

975.  Influence  of  light  upon  respiration.     It  is  not  yet  known 
positively  whether  light  has  any  effect  upon  respiration.      In 
some  experiments  there  has  been  a  slight  increase,2  in  others  a 
diminution,8  in  the  rate,  with  increased  illumination ;  but  it  is 
not  certain  whether  all  other  factors  were  excluded. 

If  the  produced  carbonic  acid  does  not  escape  readily  from  the 
tissues,  respiration  goes  on  more  slowly.4 

976.  Periods  of  rest.     Although  all  plants  require  oxygen  for 
the  performance  of  their  normal  functions,  it  by  no  means  follows 
that  when  a  plant  is  supplied  with  oxygen  the  normal  activities 
will  be  necessarily  exhibited.     In  the  case  of  certain  bulbs,  seeds, 
etc.,  even  with  the  most  favorable  surroundings,  there  ma}'  be 
no  signs  of  respirator}7  or  other  activity  until  after  the  lapse  of 

1  Rischawi:  Versuchs-Stationen,  xix.,  1876,  p.  338. 

2  Wolkoff  and  Mayer :  Landwirthschaftliche  Jahrbiicher,  1874,  Heft  iv. ; 
Cahours:  Cornptes  Rend  us,  Iviii.,  1864,  p.  1206. 

8  Dumas:  Annales  de  Chimie  et  de  Physique,  ser.  5,  tome  iii.,  1874, 
p.  105  ;  Borodin :  Just's  Botan.  Jahresbericht,  iv.,  1878,  p.  920. 

*  For  the  bearings  of  this  uppn  alcoholic  fermentation,  which,  according  to 
Melsens,  is  not  arrested  until  a  pressure  of  25  atmospheres  of  carbonic  acid 
is  reached,  see  Pasteur :  Annales  de  Chimie  et  de  Physique,  ser  3,  tome  Hi., 
1858,  p.  415;  and  Nageli:  Die  niederen  Pilze,  1877,  p.  31. 

Alcoholic  Fermentation.  This  process  is  so  intimately  connected  with 
that  of  respiration  that  it  requires  a  brief  description  at  this  point.  Reduced 
to  its  simplest  terms,  it  consists  of  the  changes  which  are  produced  in  a  solu- 
tion of  sugar  by  the  growth  of  a  microscopic  organism.  This  is  some  one  of 
the  Saccharomycetes  (a  group  of  low  fungi  which  are  propagated  by  a  process 
of  budding).  By  the  growth  of  this  fungus  the  solution  of  sugar  is  broken  up 
into  various  products,  the  most  noteworthy  being  alcohol  and  carbonic  acid. 
24 


370      CHANGES   OF    ORGANIC   MATTER   IN   THE   PLANT. 

a  given  period  of  time.  There  is  little  doubt  that  this  refusal 
of  the  resting  part  to  start  is  an  inherited  trait  connected  in 
some  way  with  the  protection  of  the  plant  against  untoward 
influences. 

977.  Respiration   is  accompanied   by   an   evolution   of  heat. 
The  flowers  of  the  melon  and  tuberose  were  examined  by  Saus- 
sure,  who  found  that  in  the  opening  of  the  former  there  was 
an  elevation  of  4  to  5  C.°,  in  that  of  the  latter,  .3°.     Caspary 
detected  a  noticeable  rise  of  temperature  in  the  opening  flowers 
of  Victoria  regia,  and  the  same  has  been  observed  in  flowers  of 
species  of  Cactus. 

978.  In  those  cases  where  it  is  possible  to  examine  an  organ 
in  which  the  process  of  respiration  is  rapid,  as  in  a  compact 
cluster  of  flowers  of  Aracese,  the  difference  between  the  tem- 
perature of  the  air  outside  and  that  inside  the  spathe  is  ver}r 
marked. 

979.  The  following  results  by  Senebier,   obtained  by   two 
methods  of  experimenting,  are  very  instructive,  showing   the 
remarkable  and  rapid  changes   of  temperature  in  such   cases. 
The  plant  in  this  instance  was  Arum  maculatum. 

Temperature  of  air.          Temperature  of  spathe. 

16.1 

17.9 

19.8 

21. 

21.8 

21.2 

18.5 

15.7 

14.1 

Even  higher  differences  have  been  observed. 

980.  Light  is  produced  during  the  growth  of  certain  of  the 
lower  fungi  under  certain  conditions.     The  phenomenon  called 
phosphorescence  is  not  known  in  any   of  the  higher  plants.1 
According  to  Fabre,  it  is  associated  with  the  absorption  and 
consumption  of  ox}*gen,  and  the  evolution  of  carbonic  acid. 

981.  Intramolecular  respiration.    Under  certain  circumstances 
plants  can  continue  to   give   off  carbonic  acid  when   no  free 
oxygen  is  supplied,  and  when  they  are  kept  in  an  atmosphere 

1  For  an  account  of  supposed  cases  of  luminous  flowers  see  Balfour's  Class 
Book  of  Botany,  1854,  p.  676. 


5 

14  7         .          ... 

5f 
64- 

15  

15 

6| 

7 

14.9     
14  3 

101 

15  

14 

5       A. 

M.                                  .      14.1      . 

INTRAMOLECULAR    RESPIRATION.  371 

of  some  other  gas.1      The  following  experiment  will  illustrate 
this :  — 

If  a  mass  of  active  seedlings  be  placed  in  a  current  of  some 
neutral  gas,  for  instance  nitrogen,  the  seedlings  will  continue  to 
evolve  carbonic  acid.  Since  the  amount  of  carbonic  acid  given 
off  is  greater  than  can  be  derived  from  the  oxygen  which  might 
be  fairly  assumed  to  have  been  retained  in  the  plants  at  the  be- 
ginning of  the  experiment,  the  conclusion  has  been  drawn  that 
the  production  of  this  gas  is  at  the  expense  of  substances  within 
the  tissues  containing  combined  oxygen.  In  other  words,  this 
process,  which  is  like  respiration  in  some  particulars,  differs  from 
it  in  this  respect :  in  ordinary  respiration  free  oxygen  enters  into 
the  plant  and  there  oxidizes  certain  matters ;  while  in  this  case 
the  molecules  of  certain  compounds  break  up,  and  the  released 
oxygen  at  once  forms,  with  carbon,  carbonic  acid,  which  is 
evolved.  This  process  is  known  as  intramolecular  respiration. 

982.  Wortmann 2  has  proved  that  when  seedlings  of  Vicia  Faba 
are  placed  for  short  periods  in  an  atmosphere  free  from  oxygen, 
the}*  give  off  the  same  amount  of  carbonic  acid  as  they  do  when 
oxygen  is  furnished.     Hence  he  was  naturally  led  to  believe  that 
all  the  carbonic  acid  produced  by  plants  has  its  origin  in  intra- 
molecular respiration,  and  that  the  free  oxygen  of  the  air  takes 
no  direct  part  in  the  formation  of  the  carbonic  acid  evolved. 

983.  But,  on  the  other  hand,  Wilson8  has  shown  that  most 
plants  evolve  much  larger  quantities  of  carbonic  acid  when  free 
oxygen  is  provided,  and  that  Vicia  Faba  forms  a  remarkable 
exception  to  this  rule.     His  experiments  were  made  upon  seed- 
lings, buds,   leaves,   flowers,   fruits,   and  cryptogamous  plants, 
and  with  uniform  results.     He  cites  Pfeffer  as  saying:  "If  an 
equal  amount  of  carbonic  acid  were  formed  in  both  intramolecu- 
lar and  normal  respiration,  this  would  only  prove  that  the  same 

1  The  same  phenomenon  has  been  observed  in  the  case  of  some  of  the 
lower  animals :  Pfliiger  (Archives  fur  Physiologic,  x.,  1875,  p.  251)  has  shown 
that  when  these  animals  are  kept  in  an  atmosphere  of  nitrogen,  they  evolve 
during  the  first  few  hours  nearly  the  same  amount  of  carbonic  acid  as  if  they 
had  been  placed  in  common  air.     The  chemical  processes  which  cause  the 
production  and  evolution  of  carbonic  acid  in  the  absence  of  free  oxygen  are 
grouped  by  Pfliiger  under  the  term  intramolecular  respiration. 

2  Arbeiten  des  botanischen  Instituts,  Wiirzburg,  1880,  p.  500. 

8  Flora,  1882,  and  American  Journal,  xxiii.,  1882,  p.  423.  For  an  interesting 
account  of  the  literature  of  intramolecular  respiration  see  Pfliiger's  paper,  men- 
tioned above.  Observations  upon  the  subject  were  made  even  during  the  last 
century  and  early  in  the  present  century.  For  Broughton's  and  Pfeffer's  work 
see  Botanische  Zeitung,  1870,  and  Pflanzenphysiologie. 


372      CHANGES   OF   ORGANIC   MATTER   IN  THE    PLANT. 

number  of  carbon  affinities  for  oxygen  had  been  satisfied  in 
each  case,  and  would  in  no  way  indicate  from  whence  the  supply 
of  oxygen  came.  And  in  case  free  oxygen  was  active  in  normal 
respiration,  in  intramolecular  respiration,  when  free  oxygen  was 
absent,  its  full  supply  might  still  be  obtained  through  constant 
powerful  attractive  forces  which  could  take  oxygen  from  other 
combinations  and  thus  give  rise  to  secondary  changes." 

984.  Eriksson l  has  shown^that  a  slight  elevation  of  tempera- 
ture occurs  during  intramolecular  respiration,  amounting  in  the 
case  of  a  mass  of  seedlings,  flowers,  or  fruits,  125  cc.  in  bulk, 
to  .l°-.3°  C.     In  the  experiments  which  he  made  with  yeast,  he 
obtained  a  much  larger  increase  of  temperature.     Thus,  when  he 
employed  500  cc.  of  a  fluid  containing  five  parts  b}-  weight  of 
water  and  one  part  by  weight  of  yeast,  together  with  10  per  cent 
of  sugar,  he  obtained  an  increase  of  3°. 9  C.     He  found,  further, 
that  in  intramolecular  respiration,  both  in  the  case  of  germina- 
tion and  in  that  of  yeast,  the  elevation  of  temperature  can  be 
noticed  for  one  week.     After  this  time,  with  diminution  of  the 
respiration,  the  temperature  becomes  the  same  as  the  surround- 
ing air ;  but  even  then  life  is  not  extinct. 

985.  The  curious  experiment  of  introducing  the  smallest  pos- 
sible amount  of  organized  ferment  into  a  liquid  from  which  all 
air  has  been  expelled,  but  which  is  otherwise  fitted  to  undergo 
fermentation  or  putrefaction,  has  resulted  in  setting  up  one  or 
the  other  of  these  processes,  and  causing  the  liberation  of  con- 
siderabje  quantities  of  carbonic  acid.     It  is  believed  that  in  this 
case  likewise  the  needed  oxygen  is  supplied  bj*  that  in  the  mole- 
cules of  ox3*gen-compounds,  which  are  easily  broken  down. 

986.  While  the  non-nitrogenous  compounds  are  those  which 
play  the  most  important  part  in  furnishing  material  for  oxidation 
and  the  release  of  energy,  the  nitrogenous  matters  share  in  this 
activity.     Some  physiologists 2  look  upon  the  latter  as  the  chief 
matters  concerned  in  the  process  of  respiration,  and  would  regard 
the  non-nitrogenous  compounds  as  merely  supplying  waste.    Ac- 
cording to  this  view,  asparagin  is  a  waste  product  somewhat 
analogous  to  urea  in  animal  economy. 

987.  From  what  has  been  said,  it  is  plain  that  respiration  does 
not  consist  merely  in  the  direct  absorption  of  oxygen  and  the 
immediate  oxidation  of  compounds  within  the  organism,   but 
that  it  is  a  complicated  process  of  which  the  absorption  of  oxy- 
gen and  the  evolution  of  carbonic  acid  are  the  extreme  terms. 

1  Untersuchungen  aus  dem  bot.  Inst.  zu  Tubingen,  1881,  p.  105. 
8  Borodin  :  Botanische  Zeitung,  1878. 


CHAPTER  XII. 

VEGETABLE  GROWTH. 

988.  As  already  shown,  vegetable  growth  consists  (1)  in  the 
formation  of  new  cells,  (2)  in  the  increase  in  size  of  previously 
existing  ones,  or,  (3)  as  is  commonly  the  case,  in  both  of  these 
processes  taking   place  simultaneously.     In  the  production  of 
new  cells  and  in  the  augmentation  of  cells  in  size  there  are  cer- 
tain chemical  and  physical  phenomena  which  always  accompany 
the  morphological  changes. 

989.  The  chemical  changes  are  essentialty  those  which  have 
been  described  under  Transmutation  and  Respiration  ;   available 
matters  change  their  character  in  order  to  be  utilized  in  the  for- 
mation and  increase  in  size  of  cells.     The  physical  phenomena 
are  chiefly  those  which  accompany  oxidation  ;  namely,  the  evolu- 
tion of  heat  and  the  production  of  electrical  disturbances. 

990.  The  materials  used  by  the  plant  for  the  formation  of  new 
structures  are  produced  by  assimilation ;  and  in  annuals  a  large 
part  of  the  assimilated  matter  is  consumed  in  growth  as  soon 
as  it  is  made.     But,  in  perennials,  especially  in  those  which 
belong  to  climates  where  vegetation  has  periods  of  rest,  a  por- 
tion of  the  assimilated  matter  is  stored  up  for  future  use.     The 
rapidity  of  the  growth  from  buds  in  the  spring  is  due  to  the 
abundant  supply  of  assimilated  matters  prepared  during  the  pre- 
ceding summer. 

991.  Hence  growth  is  not  necessarily  associated  with  increase 
in  weight.     In  fact,  in  the  growth  of  new  parts  from  a  bulb  or 
tuber,  although  there  is  a  marked  increase  of  volume,  there  is,  at 
first,  an  actual  loss  of  dry  substance  through  oxidation.     More- 
over, one  part  may  grow  at  the  expense  of  another ;  and  we  may 
have  under  certain  conditions  the  anomaly  of  an  increase  in 
volume  of  new  organs,  with  simultaneous  but  larger  decrease  in 
size  of  older  parts,  so  that  the  result,  as  regards  the  whole,  is 
diminution  of  weight. 

992.  Morphological  changes  in  the  cells.     The  two  processes 
involved  in  ordinary  growth,  namely,  increase  of  cells  in  number 
and  in  size,  may  go  on  together.     But  growing  cells  belong  to 


374  VEGETABLE   GROWTH. 

one  of  two  classes :  either  the}"  are  capable  of  producing  other 
cells,  or,  incapable  of  this,  they  develop  into  cells  for  some 
special  office.  To  the  former  class  belong  all  merismatic  tissues  ; 
(see  201)  from  the  latter  all  the  permanent  tissues  are  derived. 
Since  growing  cells  have  such  different  destinies,  we  must  ex- 
amine them  in  their  earliest  stage  to  find  what  they  have  in 
common. 

993.  The  simplicity  of  structure  in  many  of  the  lower  plants  is 
so  great  that  a  living  cell  can  be  kept  under  observation  through- 
out its  various  stages,  and  through  its  transparent  wall  all  the 
changes  which  go  on  within  it  can  be  noted.     But  the  points  of 
growth  in  most  plants,  especially  those  of  the  higher  grade,  are 
hidden  by  more  superficial  cells  ;  and  upon  removal  of  these  pro- 
tecting parts,  pathological  changes  are  brought  about  at  once, 
from  exposure  and   mechanical  injury,  and  healthy  growth   is 
arrested.      In  a   few  instances  onty,   such  as   plant-hairs  and 
other  epidermal  structures,  is  it  possible  to  observe  directly  the 
progress  of  cell-division.     Growth  in -deeper  parts  must  be  ex- 
amined by  an  indirect  method  ;  that  is,  like  parts  must  be  com- 
pared at  different  stages  of  development,  care  being  taken  to 
select  those  which  have  been  kept  under  nearly  the  same  ex- 
ternal conditions.     By  judicious  selection  of  material  for  the 
examination  of  growth,  specimens  can  be  found  which  exhibit 
in  a  single  section  several  different  phases  of  cell-division. 

994.  When  fresh  material  is  employed,  the  sections  are  so 
much  distorted  that  it  is  difficult  to  secure  satisfactory  results ; 
in  fact,  the  discordant  views  relative  to  the  formation  of  cells  are 
largely  attributable  to  this  source  of  error.     If,  however,  the 
tissue  to  be  examined  is  placed  for  a  while  in  absolute  alcohol, 
either  with  or  without  a  little   chromic  acid,  the   cell-wall   is 
rendered  so  much   harder  that  the  sections   are  not  seriously 
distorted,  and  the  contents  of  the  cells  are  more  clearly  seen. 
When  the  treatment  is  supplemented  b}-  the  use  of  staining 
agents  adapted  to  special  cases,  the  course  of  development  of 
new  cells  can  be  followed  out  with  comparative  certainty. 

995.  In  the  protoplasm  of  nearly  all  vegetable  cells  there  is  a 
spheroidal  or  lenticular  body  apparently  denser  than  the  proto- 
plasm itself.     It  retains  the  name  nucleus,  given  to  it  by  Robert 
Brown,  who  first  called  attention  to  its  importance.    Under  ordi- 
nary circumstances  it  can  readily  be  detected  in  all  active  cells 
of  the  higher  plants. 

When   living,  it  resists,  like  the   protoplasm  in  which  it   is 
embedded,  the  entrance  of  all  coloring  agents  ;  but  when  dead  it 


STRUCTURE   OF   THE   NUCLEUS.  375 

is  at  once  tinged  by  them.  Upon  the  application  of  iodine  it 
becomes  deeper  brown-yellow  than  protoplasm,  and  this  led 
Hofmeister  to  the  belief  that  it  is  richer  in  albuminoidal  mat- 
ters.1 Its  behavior  with  digestive  fluid  and  other  reagents  indi- 
cates that,  like  the  nucleus  in  the  animal  kingdom,2  it  contains 
a  substance  rich  in  phosphorus.8 

996.  The   surface   of  the   nucleus   generally   appears   to   be 
firmer  and  more  highly  refringent  than  the  interior  mass,  and  in 
these  respects  is  like  the  superficial  layer  of  protoplasm.     Even 
with  low  powers  of  the  microscope  and  without  reagents   the 
inner  mass  of  the  nucleus  is  often  seen  to  be  far  from  homo- 
geneous, generally  containing   granules,   which   are   sometimes 
irregular,    sometimes   regular   in   form.      When  a  single  large 
granule  is  present,  it  is  known  as  the  nucleolus ;  when  two  or 
more,  the  nucleoli.     These  vary  widely  in  number,  size,   and 
shape.     Besides  such  granules,  vacuoles  are  frequently  present. 
Upon  the  application  of  suitable  staining  agents,   and  by  the 
use  of  high  powers,  the  nucleus,  formerly  thought  to  be  nearly 
homogeneous,  is  shown  to  be  a  basic  substance  possessing  a 
finely  reticulated  structure.     At  times  the  nucleus  appears  to 
be  simply  dotted  throughout  with  fine  points. 

997.  When  the  bodies  which  are  associated  with  its  basic  sub- 
stance are  granular,  they  are  distinct  from  each  other  ;  but  when 
in  the  shape  of  rods,  fibres,  or  delicate  threads,  they  are  usually 
conjoined  to  form  a  sort  of  network,  or  so  connected  together 
as  to  make  a  long  thread  which  is  tangled  in  a  complicated  man- 
ner.    The  basic  substance  of  the  nucleus,  less  highly  colored  by 
staining  agents  than  the  rest,  has  been  called  Achromatin ;  while 
the  portions  which  take  color  readily  are  termed  Chromatin  by 
Flemming,  nuclein 4  by  Strasburger. 

During  cell-division  these  portions  of  the  nucleus  undergo 
remarkable  changes  of  shape  and  position,  which,  with  the 
changes  observable  in  the  nucleus  as  a  whole,  can  be  illustrated 
by  a  few  special  cases  taken  from  Strasburger's  treatise,  and 
given  in  nearly  his  words. 


1  Hofmeister:  Die  Lehre  von  der  Pflanzenzelle,  1867,  pp.  78,  79. 

a  Hoppe-Seyler:  Physiologische  Chemie,  i.  p.  84,  which  contains  a  good 
account  of  the  literature  of  the  subject. 

8  Zacharias  :  Botanische  Zeitung,  1881,  p.  169. 

*  The  only  objection  to  the  term  nuclein  is  its  previous  application  to  the 
proximate  chemical  substance  rich  in  phosphorus  which,  although  a  part  of 
the  nucleus,  is  not  proved  to  be  identical  with  the  part  which  receives  colors 
most  deeply. 


376 


VEGETABLE   GROWTH. 


998.  Development  of  stomata.  Each  of  the  mother-cells  from 
which  the  guardian-cells  of  stomata  are  formed  contains  at  first  a 
large  nucleus  with  one  large  nucleolus  or  several  small  nucleoli 
(Fig.  164,  No.  1).  The  nucleus  grows  in  size  and  becomes  gran- 
ular, but  does  not  lose  its  identity  in  the  protoplasmic  mass  (Fig. 
164,  Nos.  2,  3).  At  this  period  faint  stripes  appear  which  con- 
verge towards  the  poles  of  the  spheroidal  nucleus,  while  there  is 
developed  midwa3r,  at  what  has  been  well  called  the  equator,  a 
row  of  granules  lying  in  one  plane  and  forming  a  sort  of  disc 
or  plate  (Fig.  164,  No.  4).  The  granules  next  pass  for  the  most 
part  in  the  meridian  lines  towards  the  poles,  and  there  accumu- 
late to  constitute  new  nuclei  (Fig.  164,  No.  5).  The  polar  masses 


are  connected  by  faint  stripes,  and  from  this  stage  (Fig.  164, 
No.  6)  go  rapidly  to  their  fuller  development.  In  them  rods 
appear  which,  though  somewhat  curved,  generally  lie  in  the 
direction  of  the  axis  of  the  spindle,  and  the  contour  of  the  two 
masses  becomes  clearly  defined  (Fig.  164,  No.  7).  Next,  the 
faint  stripes  thicken  somewhat,  while  at  the  equator  there  is 
developed  a  plane  of  minute  granules  (Fig.  164,  No.  8),  which 
become  confluent  and  form  a  coherent  film.  This  soon  splits 
into  halves  between  which  cellulose  is  secreted.  At  first  the 
secretion  takes  place  in  spots,  but  it  soon  becomes  uniform. 
The  splitting  of  the  film  for  the  formation  of  the  cellulose  is 
similar  to  that  of  the  nuclear  disc,  except  that  in  the  former  the 

FIG.  164.  Changes  in  the  nucleus  during  cell-division  in  the  mother-cell  of  a  stoma 
of  Iris  pumila.  The  dark  parts  in  all  the  figures  represent  the  nuclein.  In  No.  9 
the  cell-division  is  complete.  (Strasburger.) 


CELL-DIVISION.  377 

separation  is  very  slight.  At  the  time  of  the  formation  of  the 
cellulose  film  certain  nuclear  threads  may  stretch  as  far  as  the 
wall  of  the  mother-cell ;  but  often  they  do  not  extend  to  it,  and 
in  this  case  the  gap  is  filled  out  by  a  corresponding  plate  from 
the  protoplasm.  The  cellulose  film  is  produced  almost  simul- 
taneously throughout  the  whole  extent  of  the  mother-cell,  which 
is  cut  into  two  guardian-cells,  forming  a  stoma  (Fig.  164,  No. 
9).1  Although  the  process  goes  on  without  interruption,  it  may 
be  divided  into  three  phases ;  namely,  (1)  the  arranging  of  the 
nucleolar  bodies  to  form  a  disc  in  the  middle  plane  of  the  nucleus  ; 
(2)  the  splitting  of  the  nuclear  disc  into  two  parts  which  pass 
over  towards  the  poles,  there  becoming  new  nuclei,  leaving  faint 
meridional  lines  connecting  them  ;  (3)  the  thickening  of  these 
lines,  and  the  appearance  of  granules  at  the  equator,  so  as  to 
form  a  plate  which  divides  into  halves.  The  cellulose  film 
secreted  between  these  halves  sooner  or  later  goes  across  the 
cell  cavity,  making  a  partition-wall  between  two  new  cells. 

The  mother-cell  from  which  guardian -cells  are  developed  in 
the  manner  just  described  is  itself  produced  in  nearty  the 
same  manner  from  an  epidermal  cell.  The  latter  contains  a 
spherical  nucleus  having  a  diameter  about  two  thirds  that  of 
the  cell.  It  is  not  wholly  filled  with  protoplasm,  as  is  usually 
the  case  with  cells  capable  of  division,  but  has  a  very  thick 
lining  of  protoplasm  along  the  wall,  and  in  this  the  nucleus 
is  embedded.  The  nucleus  extends  completely  across  the  cell- 
cavity,  while  above  it  and  below  it  is  cell-sap.  If,  now,  the 
epidermal  cell  is  to  give  rise  to  a  new  one,  the  nucleus  passes 
over  to  one  end  of  it  and  there  divides  into  two  parts,  essential!}' 
as  before  described,  except  that  the  halves  remain  close  together. 
Between  these  new  nuclei  the  cell  disc  or  plate,  and  the  cellulose 
plate,  are  successively  produced,  cutting  the  old  cell  into  unequal 
parts. 

999.  The  division  of  cells  in  cambium  was  examined  by  Stras- 
burger2  in  young  shoots  of  Pinus  sylvestris,  which  had  completed 
their  growth  in  length  and  had  begun  to  thicken.  These  were 
selected  on  account  of  their  rapid  development.  The  cambium 
cells  of  this  pine  have  a  lining  of  protoplasm,  together  with  a 
nucleus  which  occupies  the  middle  of  the  cell  and  completely 
fills  the  smaller  diameter.  The  nucleus  is  nearly  spherical,  or 


1  Strasburger  :   Ueber  Zellbildung  und  Zelltheilung,  1876,  p.  110.      This 
account  is  somewhat  but  not  essentially  different  in  the  edition  of  1880. 

2  Ueber  Zellbildung  und  Zelltheilung,  1876,  p.  116. 


378 


VEGETABLE   GROWTH. 


somewhat  lengthened  in  the  direction  of  the  long  axis  of  the  cell, 
and  contains  several  nucleoli.  When  it  begins  to  grow,  these 
nucleoli  disappear,  and  the  characteristic  striation  previously  de- 
scribed appears  transverse  to  the  direction  of  future  division  and 
of  the  nuclear  disc.  The  latter  is  not  clearly  defined,  and  its 
halves  do  not  recede  from  one  another  very  far,  since,  in  fact, 
there  is  not  space  for  much  expansion  in  any  event.  The  parti- 
tion wall  at  first  is  confined  to  the  space  between  the  halves, 
and  these  are  found  in  close  contact  with  it,  but  later  it  extends 


completely  across.  The  remarkable  thickness  of  the  radial  walls 
of  the  cambium  is  explained  by  Sanio  as  due  to  the  non-absorp- 
tion of  a  part  of  the  mother-cell ;  but  Strasburger  ascribes  it 
to  the  uninterrupted  nutrition  of  the  radial  wall  from  the  contents 
of  the  cell  itself.  The  newly  formed  partition-wall  is  thin,  and 
cannot  be  shown  by  reagents  to  be  double.1 


1  The  student  should  consult  Strasburger's  work  :  Ueber  den  Theilungs- 
vorgang  der  Zellkerne,  1882  ;  also  Das  botanische  Practicum,  chap,  xxxiv. 

FIG.  166.  Behavior  of  nucleus  during  cell-division  In  the  endosi>erm  of  Allium  to 
illustrate  the  extraordinary  complexity  of  the  stained  bodies.  The  dark  lines  represent 
the  chromatin.  (Flemming.) 


DEVELOPMENT   OF    POLLEN-GRAINS. 


379 


1000.  Development  of  pollen-grains.  This  affords  some  of  the 
most  instructive  examples  of  cell-division,  and  owing  to  the 
facility  with  which  material  can  be  procured  and  studied,  has 
received  much  attention. 

(1)  Superficial  phenomena.  These,  which  can  be  easily 
traced  without  the  employment  of  staining  agents,  are  in  brief 
as  follows :  At  the  period  when  the  loculi  of  the  anthers  begin 
as  minute  elevations  at  the  end  of  the  stamen,  the  external 
layer  of  cells,  which  is  to  serve  as  epidermis,  is  underlaid  by 


a  group  of  small  cells  which  give  rise  to  the  mother-cells  of  the 
pollen  and  to  the  lining  of  the  anther  itself.  This  group  is 
termed  the  archesporium ;  by  division  of  its  inner  layer,  large 
mother-cells  are  produced  which  divide  to  form  the  pollen- 
grains.  The  division  of  a  mother-cell  may  give  rise  to  two,  three, 
or  four  pollen-grains,  and  in  some  cases  more,  according  to  the 

FIG.  166.  Fritillaria  Persica.  Division  of  the  mother-cells  of  pollen,  a,  early  stage, 
in  which  the  threads  are  confused;  b,  the  segments  in  course  of  longitudinal  division; 
c,  the  nuclear  spindle  in  profile;  d,  the  same  seen  from  its  extremity  or  pole;  e,  division 
of  the  nuclear  plate ;  /,  separation  of  the  derivative  or  daughter-segments ;  g,  formation 
of  the  derivative  tangles  and  the  cell-plate;  A,  the  course  of  the  nuclear  threads  in  the 
derivative  nuclei;  i,  longitudinal  extension  ;  /.^nuclear  spindle,  on  the  right,  in  profile, 
on  the  left,  from  its  extremity  ;  /,  separation  of  the  segments,  on  the  left  seen  in  pro- 
file, on  the  right  from  the  extremity  ;  m,  formation  of  the  cell-plates.  (Strasburger.) 


380  VEGETABLE   GROWTH. 

direction  of  the  lines  of  fission.  It  is  possible  to  distinguish 
differences  in  the  mode  of  division  which  are  fairly  charac- 
teristic of  Angiosperms  and  Gymnosperms,  of  Monocotyledons 
and  Dicotyledons.  Although  the  morphology  of  the  tissues 
involved  and  the  course  of  development  are  not  yet  completely 
understood,  it  may  be  said  that  the  formation  of  pollen-grains 
suggests  throughout  the  mode  in  which  the  male  elements  are 
produced  in  the  higher  cryptogams. 

(2)  Changes  in  the  Nucleus.  The  following  suggestions  by 
Strasburger  for  demonstrating  the  nuclear  changes  in  pollen- 
grains  can  be  applied  with  few  modifications  to  all  cases  of  cell- 
division  :  Place  the  young  part,  in  this  case  a  very  young 
anther,  in  a  solution  of  methyl-green  in  acetic  acid,  and  subject 
it  to  slight  pressure  by  which  the  contents  of  the  anther-cells 
will  be  discharged.  Those  parts  susceptible  of  staining  will  take 
the  color  readily  and  the  different  stages  can  be  followed  out  sub- 
stantially as  shown  in  the  figures.  For  the  staining-agent  above 
mentioned  the  following  ma}'  be  substituted,  —  gentian-violet  in 
acetic  acid,  or  nigrosin  with  picric  acid.  Preparations  made  witli 
the  latter  can  be  preserved  in  glycerin  without  losing  color. 

Another  and  better  method  is  to  place  sections  of  the  tissue 
which  has  been  kept  for  a  few  days  in  absolute  alcohol,  in  an 
alcoholic  solution  of  safranin,  and  after  twelve  hours  wash  with 
absolute  alcohol ;  then  transfer  them  to  oil  of  origanum  and 
thence  to  a  thick  solution  of  Dnmar  in  turpentine,  for  mounting. 

By  the  safranin  the  delicate  threads  of  the  spindle  are  not 
much  colored  ;  they  take,  however,  a  good  color  with  haematoxj-- 
lin.  Other  combinations  of  coloring  agents  give  good  results.1 

1001.  Cell-division  in  plant-hairs.     The  stamen-hairs  of  Tra- 
descantia  Virginica  afford  excellent  material  for  this  examina- 
tion.    The  last  or  upper  three  cells  while  still  young  are  capable 
of  division.     If  the  very  young  hairs  are  transferred  carefully  to 
a  slide  on  which  is  a  three  per  cent  solution  of  cane-sugar,  they 
will  continue  the  process  of  cell-division  as  shown  in  Fig.  167. 
If  the  specimen  is  a  good  one,  and  has  not  been  much  injured 
during  its  removal,  it  will  remain  active  for  several  hours. 

All  the  examinations  of  cell-division  require  the  use  of  high 
powers  of  the  microscope,  none  being  better  for  the  purpose 
than  the  so-called  homogeneous  immersion  lenses. 

1002.  The  direction  in  which  the  new  cell- wall  is  laid  down  at 
the  point  of  growth  has  been  exhaustively  examined  by  Sachs. 

1  Pas  botanische  Practicum,  1884,  p.  598. 


DIRECTION   OF   CELL-DIVISION. 


381 


According  to  him,  the  planes  of  the  walls  at  a  point  ,of  growth 
may  be  thus  classified : 1  — 


1  "  The  relations  of  the  periclinal  and  anticlinal  planes  are  illustrated  by 
the  following  cases  :  — 

(a)  If  the  outline  (in  longitudinal  section)  of  the  growing  point  is  a  parab- 
ola, the  periclinals  will  constitute  a  system  of  confocal  parabolas  of  different 
parameter,  the  focus  of  the  system  being  at  the  point  of  intersection  of  two 
lines,  of  which  one  is  the  direction  of  the  axis  and  the  other  of  the  parameter. 
In  this  case  the  anticlinals,  being  the  orthogonal  trajectories  of  the  periclinals, 
constitute  a  system  of  confocal  parabolas,  the  axis  and  focus  of  which  coincide 
with  those  of  the  periclinals. 

(b)  If  the  outline  of  the  growing  point  is  a  hyperbola,  the  periclinals  will 
be  confocal  hyperbolas,  with  the  same  axis  but  different  parameter  ;  the  anti- 
clinals will  be  confocal  ellipses,  with  the  same  focus  and  axis  as  the  periclinals. 

(c)  If  the  outline  of  the  growing  point  is  an  ellipse,  the  periclinals  will  be 
confocal  ellipses  ;  the  anticlinals  will  be  confocal  hyperbolas  "  ( Abstract  from 

FIG.  167.  Tradescantia  Virginica.  Process  of  cell-division  in  the  stamen-hairs. 
a,  with  a  quiescent  nucleus  in  the  lower  cell,  and  in  the  upper,  one  which  has  just  fin- 
ished its  division ;  b,  nucleus  showing  a  coarse  granular  structure  with  a  tendency  to 
linear  arrangement  of  the  particles.  The  drawings  from  c  to  k  inclusive  exhibit  the 
different  stages  of  cell-division  at  the  following  points  of  time:  c,  at  10  o'clock  and  10 
minutes;  d,  10.20;  e,  10.25;  /,  10.30;  g,  10.35;  h,  10.40;  i,  10.50;  j,  11.10;  k,  11.30- 
(Strasburger.) 


382 


VEGETABLE   GROWTH. 


1.  Periclinal,   those   which    exhibit   in   longitudinal   section 
curves  in  the  same  direction  as  the  surface. 

2.  Anticlinal,  those  which  cut  the  surface  and  the  periclinal 
walls  at  right  angles  (forming  a  system  of  orthogonal  trajecto- 
ries for  the  periclinal  walls). 

3.  Radial,  those  which  pass  through  the  axis  of  growth  and 
cut  the  surface  at  right  angles. 

4.  Transverse,  those  which  cut  both  the  axis  of  growth  and 
the  surface  at  right  angles. 

1003.  Growth  of  the  cell- wall.  When  the  new  cell  is  formed 
it  undergoes  changes  in  size,  and  often  in  shape  and  thickness. 
If  it  increases  in  size  regularly  at  all  points  of  the  surface,  it 

preserves,  of  course,  its 
original  shape  ;  but  if  its 
growth  is  irregular  at 
different  points,  great 
modifications  of  form  re- 
sult. Pollen-grains  afford 
instances  of  the  former 
method  of  growth,  while 
the  latter  is  seen  in  the 
multicellular  organs,  for 
example  stems  and  leaves. 
At  the  growing  points  of 
the  stem  and  leaf  the 
cells  when  first  formed  are 
nearly  alike  in  appear- 
ance ;  but  wide  differ- 
ences are  soon  presented. 
The  growth  of  a  cell 
in  size  may  be  terminal, 
when  it  gives  rise  to 
elongated  forms ;  or  lo- 
calized at  a  point,  line, 
or  zone,  \yhen  projections 
and  swellings  of  various  kinds  are  produced.1 

Arbeiten  des  botan.  Inst.  in  Wiirzburg,  1878,  in  appendix  to  Text-book,  2d 
Eng.  ed.,  p.  951). 

The  student  should  also  read  Sachs's  Vorlesungen,  1882,  pp.  523-557. 

1  These  have  already  been  sufficiently  considered  in  the  histological  part 
of  this  volume,  and  it  is  not  necessary  to  again  call  attention  to  the  adaptations 
of  the  resultant  structures  to  their  respective  kinds  of  work  in  the  organism. 

FIG  168.  Arc-auxanometer  /,  thread  connecting  plant  with  short  arm  of  lever  a  ?. 
The  weight  of  long  arm  balanced  by  movable  weight  at  k.  (Pfeffer.) 


RECORDING  AUXANOMETERS. 


1004.  Measurement  of  growth.     In  some  cases  it  is  very  easy 
to  make  direct  measurements  of  the  amount  of  increase  in  vol- 
ume ;  but  in  general  it  is  necessary  to  employ  some  form  of  appa- 
ratus by  which  the  amount  can  be  more  or  less  exaggerated  by 
a  multiplier. 

Several  forms  of  growth- measurers,  or  auxanometers,  have 
been  devised  for  attaining  this  end.  The  simplest  consists  of 
a  fixed  arc  of  large  radius  (see  Fig.  168),  on  which  a  delicate 
arm  moves  up  or  down  according  to  the  direction  in  which  a 
small  wheel  at  the  centre,  to  which  the  arm  is  attached,  is  moved 
by  the  action  of  a  thread  fastened  to  the  plant.  Care  must  be 
taken  to  balance  the  arm  as  perfectly  as  possible,  in  order  to 
prevent  any  strain  on  the  plant  by  the  weight  of  the  index. 

This  form  of  apparatus  is  well  adapted  to  demonstration  before 
a  class ;  and  if  a  rapidly 
growing  seedling  or  strong 
scape  is  chosen  for  experi- 
ment, the  movement  of  the 
arm  through  the  arc  in '  an 
hour  will  be  sufficient  to  be 
clearly  seen  at  a  considera- 
ble distance.  A  modifica- 
tion of  the  apparatus  by 
Professor  Bessey  reduces 
its  cost  to  a  mere  trifle. 
Both  the  arc  and  its  sup- 
porting radii  are  made  of 
strong  manila  paper ;  the 
wheel  is  a  common  spool, 
and  the  arm  may  be  a  slen- 
der straight  straw. 

1005.  Recording  Auxano- 
meters.   For  the  purpose  of 
registering  growth,  several 
applications  of  the  chrono- 
graph   have    been     made. 
One  of  the  most  satisfactory 
of  these  consists  of  a  slowly 

revolving  cylinder  covered  with  smoked  paper,   upon  which  a 
needle,  attached  to  the  end  of  a  balanced  thread  passing  over  a 

FIG.  169.  Registering  auxanometer.  The  thread  attached  to  the  plant  passes  over 
the  small  wlieel  at  x,  and  is  balanced  by  a  weight.  The  index  z  is  balanced  by  the 
weight  g  ;  the  thread  between  them  goes  over  the  wheel  r.  The  cylinder  is  carried  round 
by  the  clock-work,  which  is  regulated  by  the  pendulum  weight  at  p.  (Pfeffer.) 


884  VEGETABLE  GEOWTfi. 

wheel,  leaves  its  trace  as  it  ascends  or  descends.  The  wheel  is 
caused  to  move  by  means  of  a  second  balanced  thread  which 
passes  over  its  axis,  and  which  is  fastened  at  one  end  to  the 
growing  part  of  the  plant. 

1006.  Pfeffer's  modification  of  this  apparatus  provides  that  the 
cylinder  shall  turn  a  short  distance  at  regular  intervals  of  time, 
so  that  the  line  made  by  the  needle  becomes  interrupted  and  thus 
exhibits  the  appearance  of  steps ;  in  which  the  height  of  the  step 
represents  the  total  ascent  or  descent  of  the  needle  during  a 
given  time,  while  the  other  line  of  the  step  merely  marks  the  dis- 
tance through  which  the  cylinder  moves  at  the  close  of  one  of  its 
intervals. 

1007.  Examples  of  very  rapid  growth  are  afforded  by  many 
fungi ;  for  instance  the  common  puff-ball,  which  increases  enor- 
mously in  size  during  a  single  night. 

Shoots  of  bamboo  have  been  observed  at  Kew  to  grow  at  the 
rate  of  two  to  three  inches  in  the  twenty-four  hours  ;  and  in  its 
native  habitat,  Bambusa  gigantea  has  been  known  to  grow  more 
than  ten  inches  a  day. 

The  expansion  of  the  leaves  of  Victoria  regia  is  extremely 
rapid,  under  favorable  conditions  reaching  a  foot  in  the  twenty- 
four  hours.  The  scapes  of  many  plants  develop  at  a  rapid  rate, 
and  afford  excellent  material  for  practice  with  the  auxanometer. 

1008.  Conditions  of  growth.     Vegetable  growth  does  not  take 
place  unless  there  is  an  available  supply  of  assimilated  matter, 
access  of  free  oxygen,  and  a  sufficiently  high  temperature.     The 
assimilated  matter  may  be  furnished  to  the  growing  parts  di- 
rectly from  green  tissues,  or  from  reservoirs  where  it  has  been 
stored  up.     In  either  case  it  must  come  in  a  state  of  solution  to 
the  growing  cells,  and  hence  a  certain  amount  of  water  is  re- 
quired for  the  transfer.     That  the  amount  of  water  demanded  is 
not  necessarily  large,  is  shown  by  the  starting  of  shoots  from 
bulbs,  tubers,  etc.,  in  the  spring,  even  when  no  water  has  been 
furnished  from  outside. 

1009.  Although  the  process  of  respiration  in  green  plants  may 
go  on  for  a  time  without  free  oxygen,  as  has  been  shown  by  the 
experiments  described  on  page  371,  there  is  no  proof  that  growth 
occurs  under  such  circumstances.    In  an  atmosphere  of  hydrogen, 
nitrogen,  carbonic  acid,  or  nitrous  oxide,  —  gases  which  are  not 
in  themselves  harmful  to  plants, — growth  does  not  take  place, 
as  has  been  proved  by  experiments  upon  seeds  and  seedlings. 
Detmer  has  shown  that  growth  is  immediately  checked  when  the 
plant  is  deprived  of  free  oxygen,  but  death  does  not  ensue  until 


RELATIONS  TO  TEMPERATURE. 


385 


after  a  considerable  time.  During  the  period  of  inactivity  the 
plant  is  ready  to  respond  at  once  to  the  influence  of  oxygen, 
growth  being  then  immediately  resumed. 

1010.  If  assimilated  matters  and  free  oxygen,  both  essential 
to  growth,  are  abundantly  supplied  to  a  plant  which  is  kept  at 
too  low  a  temperature,  growth  does  not  occur.      The  minimum 
limit  for  growth  is  different  for  different  plants,  and  is  not  the 
same  for  all  organs. 

Again,  it  must  be  noted  that  there  is  a  maximum  limit  of  tem- 
perature above  which  growth  does  not  take  place,  and  this  limit 
is  also  different  for  different  plants.  Between  the  lower  and 
upper  limits  there  is,  for  the  plants  which  have  been  thus  far 
studied  with  respect  to  the  effect  of  heat  on  growth,  an  optimum 
of  temperature  at  which  growth  is  most  rapid. 

1011.  Relations  of  growth  to  temperature.     The  minimum  tem- 
perature required  for  growth  is  generally  much  higher  for  plants 
of  warm  regions  than  for  plants  of  cold 

climates,  and  there  are  wide  differences 
even  among  plants  belonging  to  the  same 
climate.  A  few  of  the  earliest  spring 
plants  begin  their  growth  at  or  very  near 
the  freezing-point  of  water :  it  is  thought 
by  some  observers  that  growth  ma}7,  in 
a  few  cases,  take  place  even  below  this 
point.  Kjellmann  states  that  the  ma- 
rine algae  at  Spitzbergen  continue  to  de- 
velop their  thallus  during  the  polar  night 
of  three  months,  and  that  most  of  them 
during  this  time  produce  their  spores, 
the  temperature  of  the  sea-water  being 
on  the  average  one  degree  below  zero, 
Centigrade.1 

But,  on  the  other  hand,  many  of  the 
tropical  plants 2  cultivated  in  hot-houses 
cease  growing  when  the  temperature  falls  below  10°  or  15°  C. 

1012.  The  maximum  temperature  for  growth  is  as  wide  in  its 
range  for  different  plants  as  the  minimum.      Aside  from  the 


1  Comptes  Rendus,  Ixxx.,  1875,  p.  474.     See  also  Falkenberg :  Die  Algen 
iin  weitesten  Siune,  in  Schenk's  Botanik,  1882. 

2  See  De  Candolle  :  Physiologic  vegetale,  1832. 

PIG.  170.    Double-walled  metallic  box  for  keeping  microscopic  objects  at  a  given 
temperature  while  under  observation.    (Sachs.) 


886  VEGETABLE  GROWTft. 

instances  of  plants  growing  in  hot  springs,  it  may  be  said  to 
lie  at  or  very  near  50°  C.  The  figures  obtained  by  Sachs  for  the 
common  plants  he  experimented  upon  are  in  general  between 
36°  and  46°  C.  It  is  a  curious  fact  that  some  tropical  plants 
are  not  capable  of  bearing  a  higher  temperature  than  a  few 
plants  of  cold  countries.1 


1013.  The  optimum  temperature  for  growth  lies  in  most  cases 
between  20°  and  36°  C. 

1014.  The  following  table,  compiled  by  Pfeffer,  exhibits  at  a 
glance  the  cardinal  points   of  temperature  as  they  have   been 
determined  by  four  observers  :  — 

1  Pfeffer  :  Pflanzenphysiologie,  ii.,  1881,  p.  123. 

PIG.  171.  Apparatus  for  keeping  seedlings  in  a  constant  temperature  The  drum  at 
d  is  an  ordinary  tlierrao-regulator  by  which  the  flow  of  illuminating  gas  can  be  controlled 
within  narrow  limits.  To  insure  still  greater  control,  the  more  sensitive  regulator,  r, 
is  also  employed.  The  cylindrical  vessel,  z,  has  double  walls,  the  space  between  them 
being  filled  with  water.  Under  this  vessel  a  very  small  burner  is  sufficient  even  for 
optimum  temperature.  (Pfeffer.) 


RELATIONS  TO  LIGHT. 


387 


Name  of  Plant. 

Temperature  for  Growth. 

Observer. 

Minimum. 
°C. 

Optimum. 

Maximum. 

Triticum  vulgare  .     . 

(5.0 
{  7.5 

(28.7 
1  29.7 

42.5 

Sachs,  i 
Kbppen.2 

Hordeum  vulgare 

5. 

28.7 

37.7 

Sachs. 

Sinapis  alba    .     .     . 

0. 

(21. 

(           28.0 

De  Candolle.s 

(27.4 

\  over  37.2 

De  Vries.* 

Lepidium  sativum    . 

1.8 

(21. 

(            28. 

De  Candolle. 

J27.4 

\  below  37/2 

De  Vries. 

Li  n  inn  usitatissimum 

1.8 

(21. 

(          28. 

De  Candolle. 

(27.4 

\  over  37.2 

De  Vries. 

Trifolium  repens  .     . 

5.7 

21-25. 

below  28. 

De  Candolle. 

Phaseolus  multiflorus 

9.5 

33.7 

46.2 

Sachs. 

Pisum  sativum      .     . 

6.7 

26.6 

Koppen. 

Lupinus  albus      .     . 

7.5 

28. 

Koppen. 

(9.5 

!33.7 

46.2 

Sachs. 

ZeaMais    .... 

3  9.6 

32.4 

Koppen. 

(». 

21-28. 

35. 

De  Candolle. 

Cucurbita  Pepo    .     . 

13.7 

33.7 

46.2 

Sachs. 

Sesamum  orientale    . 

13. 

25-28. 

below  45. 

De  Candolle. 

1015.  Relations  of  growth  to  light.  It  is  only  under  the  influ- 
ence of  light  that  the  plant  can  prepare  from  inorganic  matter 

1  Text-book,  2d  Eng.  ed.,  p.  830. 

2  Warme  und  Pflanzensachsthum,  1870,  p.  43. 

8  Bibliotheque  universelle  d.  Geneve,  Archives  des  Sciences  physiques, 
xxiv.,  1865,  p.  243. 

*  Materiaux  pour  la  connaissance  de  1'influence  de  la  temperature  sur  les 
plantes,  Archives  Neerlandaises,  v.,  1870,  p.  385. 

Koppen  has  given  an  instructive  table  which  exhibits  the  relations  of 
growth  to  temperature  in  a  few  common  plants.  The  figures  denote  the  growth 
in  forty-eight  hours  of  the  whole  descending  axis  of  each  plantlet. 


Temperature. 

Lupinus 
albus. 

Pisum 
sativum. 

Vicia  Faba. 

Zea  Mais. 

Triticum 
vulgare. 

10.4 

5.5 

4.6 

14.4 

9.1 

5.0 

4.5 

17. 

11.0 

5.3 

6.9 

21.4 

25.0 

25.5 

9.3 

3.0 

41.8 

24.5 

31.0 

30.0 

10.1 

10.8 

59.1 

25.1 

40.0 

27.8 

11.2 

J8.5 

59.2 

26.6 

5t,.l 

53.9 

21.5 

29.6 

86.0 

26.5 

50.1 

40.4 

15.3 

26.5 

73.4 

30.2 

43.8 

38.5 

5.6 

64.  6 

10U.9 

31.1 

43.3 

38.9 

8.0 

49.4 

91.4 

33.6 

12.9 

8.0 

50.2 

40.3 

36.5 

12.6 

8.7 

20.7 

5.4 

39.6 

6.1 

11.2 

VEGETABLE   GROWTH. 


materials  for  its  growth  ;  but  if  an  adequate  amount  of  assimilated 
substance  has  been  stored  up,  growth  can  go  on  in  the  dark  until 
this  store  is  exhausted.  It  is,  in  fact,  in  the  dark  that  nearly 
all  vegetable  growth  takes  place.  It  is  well  known  that  all  the 
points  of  growth  in  the  ordinary  higher  plants  are  more  or  less 
protected  from  the  action  of  light.  Thus,  the  growing  tissues  of 
buds  are  concealed  beneath  external  structures ;  so  also  is  the 
cambium  by  which  dicotyledons  increase  in  thickness. 

1016.  When,. however,  a  shoot  develops  in  darkness  it  is  apt 
to  become  much  more  attenuated  than  when  it  develops  in  light ; 
its  leaves  are  etiolated,  and  of  abnormal  shape  and  diminished 
size.     Such  shoots  are  said  to  be  "  drawn." 

1017.  There  is  considerable  difference  in  the  degree  to  which 
different  parts  of  plants  are  affected  by  the  withdrawal  of  light, 
and  there  are  also  differences  in  this  respect  between  different 
species.     The  effect  of  darkness  upon  shoots  is  well  shown  by 

the  simple  experiment 
of  conducting  a  branch 
of  some  strong  plant 
like  Tropaeolum  or  a 
gourd  into  a  dark  box, 
all  its  other  leaves  be- 
ing kept  in  the  light. 
The  effects  are  more 
striking  when  the  shoot 
is  a  flowering  one ; 
the  internodes  will  be- 
come much  drawn,  the 
leaves  will  be  small 
and  blanched,  the  calyx 
will  be  pale,  but  the 
rest  of  the  flower  will 
be  hardly  affected 
either  in  shape  or  size. 
It  sometimes  happens, 
however,  that  the  flow- 
ers will  be  abnormal. 

1018.  The  relations  of  growth  to  oxygen.    All  growth  is  accom- 
panied by  the  oxidation  of  assimilated  substance,  or  food.     Can 
growth  be  stimulated  by  furnishing  to  the  plant  a  larger  amount 
of  oxygen  than  it  would  obtain  under  natural  conditions  ?    This 


FIG.  172.    Growth  of  gourd  in  light  and  darkness.    (Sachs.) 


CHANGES   IN   THE  BATE   OF   GROWTH.  389 

question  is  not  yet  positively  answered  by  any  experiments.  It 
has  been  shown  that  some  plants  grow,  for  a  time  at  least,  more 
rapidly  when  they  are  subjected  to  a  slight  increase  of  pressure  of 
the  atmosphere  by  which  they  are  surrounded  ;  but  there  are  also 
a  few  cases  which  indicate  that  some  other  plants  may  grow  more 
rapidly  under  a  diminished  pressure. 

The  "  resting"  state  of  some  plants  cannot  be  shortened  by 
an}'  increase  in  the  amount  of  oxygen  furnished ;  it  is  only  after 
the  normal  time  of  rest  has  ended  that  any  growth  begins. 
When  periods  of  rest  cannot  be  disturbed  by  any  ordinary  change 
in  the  surroundings,  they  ma}*  be  held  to  be  conservative,  since 
they  are  generally  correlated  with  the  climatic  conditions  of 
peril  from  cold  or  from  dryness,  under  which  these  plants 
naturally  live.1 

1019.  Periodical  changes  in  the  rate  of  growth.     Even  under 
external  conditions  which  are  as  nearly  constant   as   possible 
growth  is  not  quite  uniform  in  its  rate.     Thus,  an  extending 
internode  grows  in  length  at  first  slowly,  then  with  gradually 
accelerating  rapidity  until  a  maximum  of  growth   is  reached, 
from  which  point  the  rate  declines  until  with  maturity  of  the  part 
growth  ceases.     The  line  of  growth,  when  given  graphically,  is 
a  curve  known  as  the  great  curve  of  growth ;  and  the  period  of 
rise  and  decline  is  the  grand  period,  to  distinguish  this  from  the 
minor  periods  of  accelerated  growth,  which  appear  on  the  curve 
as  small  fluctuations. 

1020.  Properties  of  new  cells  and  tissues.     Newly  formed  cells 
are  generally  characterized  by  the  possession  of  a  certain  amount 
of  turgidity  ;  the  young  cell- wall  exerting  more  or  less  resistance 
to  the  expansive  contents  within.     The  contents  are  therefore 
compressed  to  some  degree  by  the  confining  wall ;    the  action 
and  reaction  varying,  of  course,  with  changes  in  the  surroundings. 
If  a  part  of  its  water  be  withdrawn  from  the  cell,  the   com- 
pression is  materially  lessened ;  while,  on  the  other  hand,  an 
increase  in  the  amount  of  water  must  augment  it. 

1021.  These  features  have  been  recently  re-examined  by  De 
Vries,  who  has  suggested  a  quantitative  method  for  determining 
the  amount  of  turgidity  at  an}*  given  time.     The  method,  when 
reduced  to  its  simplest  terms,  consists  in  the  use  of  solutions  of 


1  For  a  very  curious  account  of  experiments  upon  the  influence  of  electricity 
upon  growth,  the  student  should  see  Grandeau  :  De  1'influence  de  1'electricite 
atniospherique  sur  la  nutrition  des  vegetaux,  Annales  de  Chimie  et  de  Phy- 
sique, ser.  5,  tome  xvi.,  1879,  p.  145. 


390  VEGETABLE   GROWTH. 

salts  of  known  strength  in  which  the  tissues  are  placed,  and 
which  are  then  allowed  to  act  upon  the  contents  of  the  cells. 
When  the  solutions  are  more  dense  than  the  fluids  in  the  cavity 
of  the  cell,  an  exosmotic  action  withdraws  a  certain  amount 
of  the  water  from  the  cell,  causing  thereby  a  shrinking  of  its 
contents  which  can  be  easily  observed  under  the  microscope,  or 
noted  by  curvature  of  the  whole  section.  The  method  permits 
the  experimenter  to  ascertain  within  narrow  limits  the  density 
of  the  contents  of  a  given  cell,  and  to  determine  the  relative 
degree  of  turgidity  in  different  cases.  When  a  cell  undergoes 
no  change  of  form  upon  being  placed  in  a  solution  of  a  given 
strength,  that  solution  is  taken  as  a  measure  of  the  density  of 
its  contents.1 

1022.  Tensions  in  cell-wall.    There  may  frequently  be  observed 
a  tension  of  different  layers  of  the  cell-wall.     This  can  be  easily 
demonstrated  by  making  thin  sections  of  any  succulent  tissues 
from  which  cells  can  be  readily  detached ;  a  curvature  will  be 
detected  at  the  moment  of  cutting. 

1023.  Young  cell- walls  are  elastic  to  a  certain  extent ;  but 
their  limit  of  elasticity  is  easily  exceeded,  and  then  they  remain 
in   the   stretched   condition.     When   an   internode   is   strongly 
stretched  in  the  direction  of  its  length,  it  undergoes  permanent 
elongation.     This  elongation  may  amount  in  some  cases  to  three 
or  even  five  per  cent ;  whereas  the  temporar}-  extension  in  the 
same  instances  may  range  from  seven  to  seventeen  per  cent. 
The  extensibility  diminishes,  while  the  elasticity  increases,  with 
the  age  of  the  internode. 

1024.  From  his  experiments  Sachs  draws  the  following  con- 
clusions regarding  growing  iuteruodes :    (1)  After  flexion  they 
do  not  completely  recover  their  straightness ;  (2)  one  vigorous 
bending,  and  to  a  still  greater  extent  repeated  ones  in  opposite 
directions,  leave  the  internode  flaccid,  or  deprive  it  of  its  rigid- 
ity ;   (3)  when  growing  internodes  are  sharply  struck,  there  is 
a  sudden  curvature,  the  concavity  of  which  lies  towards  the 
direction  of  the  blow.2 

1025.  Tension  of  tissues.     Under  the  ordinary  circumstances 
of  growth  walls  of  young  cells  continue  to  be  somewhat  elastic 

1  Plasmotysis.     For  a  full  account  of  the  quantitative  action  of  numerous 
plasmolytic  agents  the  student  should  consult  De  Vries's  paper  in  Pringsheim's 
Jahrbiicher  for  1884,  where  the  effect  of  potassic  nitrate  and  other  substances 
upon  the  protoplasmic  film  is  detailed  at  length.     In  the  Laboratory  at  Cam- 
bridge, Mr.  Puffer  has  confirmed  most  of  De  Vries's  observations. 

2  Sachs  :  Text-book,  2d  Eng.  ed.,  1882,  pp.  784-788. 


TENSION   OF   TISSUES. 


391 


and  hence  exhibit  distinct  tensions.  If  there  is  a  marked  dif- 
ference in  the  rate  of  growth  between  the  internal  and  the  ex- 
ternal cells  in  any  organ,  as  is  the  case  in  most  young  stems, 
the  more  superficial  tissues  are  stretched  to  some  extent  by  the 
internal  ones ;  hence  arise  tensions  of  tissues,  the  organ  in 
this  state  being  in  a  balanced  condition,  in  which  the  equilibrium 
can  be  disturbed  by  slight  external  or  internal  causes.  The 
following  experiment  exhibits  the  phenomenon  of  tension  very 
strikingly :  From  a  long  and  thrifty  young  internode  of  grape- 
vine cut  a  piece  which  shall  measure  exactly  one  hundred  units, 
for  instance,  millimeters.  From  this  section,  which  measures 
exactly  one  hundred  millimeters,  carefully  separate  the  epi- 
dermal structures  in  strips,  and  place  the  strips  at  once  under 
an  inverted  glass  to  prevent  drying ;  next,  separate  the  pith  in 
a  single  unbroken  piece  wholly  freed  from  the  ligneous  tissue. 
Finally,  remeasure  the  isolated  portions,  and  compare  with  the 
original  measure  of  the  internode.  There  will  be  found  an 
appreciable  shortening  of  the  epidermal  tissues  and  a  marked 
increase  in  length  of  the  pith.1  The  young  ligneous  tissue  is 
generally  shortened  by  its  release,  but  this  result  is  by  no 
means  constant.  The  most  astonishing  feature  is  the  great 
difference  which  exists  between  the  length  of  the  external  tis- 
sues and  that  of  the  internal  tissues  which  up  to  the  period 
of  isolation  they  had  compressed.  The  external  parts  had  been 
plainly  stretched  to  a  certain  extent,  while  the  internal  had 
been  as  obviously  confined  by  them.  The  tensions  are  not  only 
in  the  direction  of  the  length,  but  are  also  transverse.  Similar 
tensions  are  to  be  found  also  in  foliar  organs.  But  there  are 


1  The  following  table  exhibits  the  remarkable  differences  in  tension  be- 
tween the  outer  and  the  inner  parts  of  young  shoots  of  Nicotiana  Tabacum. 
Each  internode  is  first  cut  squarely  off  at  both  ends,  and  then  carefully  sliced 
lengthwise  so  as  to  separate  the  bark,  wood,  and  pith  from  each  other.  Sup- 
posing the  length  of  the  whole  internode  to  be  one  hundred  units,  the  length 
of  the  cortex  will  fall  short  of  this,  while  that  of  the  pith  will  considerably 
exceed  it. 


Number  of  the  Internode, 
counting  from  the  youngest. 

Length  of  the  Isolated  Tissue. 

Cortex. 

Woody  part. 

Pith. 

I  -IV 

94.1 
96.9 
96.5 
99.5 

98.5 
98.9 
98.5 
99.5 

102.9 
103.5 
100.9 
102.4 

V   VII 

vni.-ix  

X.-XI  

392  VEGETABLE  GROWTH. 

some  parts,  as  for  example  most  roots  near  their  extremity, 
which  do  not  exhibit  this  phenomenon. 

1026.  Geotropism.  Suppose  a  young  shoot  to  possess  the  ten- 
sion already  described ;  let  this  be  placed,  while  growing,  in  an 
horizontal  position.  In  consequence  of  its  position  the  nutri- 
ent fluids  will,  from  the  force  of  gravitation,  have  a  tendency 
to  collect  in  greater  amount  in  the  cells  upon  its  under  side. 
Their  presence  on  that  side  will  not  only  cause  an  increase 
of  turgescence  there,  but  will  offer  to  the  growing  cells  a  larger 
amount  of  available  material  for  immediate  use  in  growth. 


especiall}-  for  laying  down  the  cell-wall.  From  one  or  from 
both  of  these  causes  there  will  therefore  be  an  appreciable  elon- 
gation of  the  tissues  on  the  under  side,  and  hence  a  curving  up- 
wards will  occur,  which  finally  results  in  the  assumption  of  the 
erect  position  by  the  organ  in  question. 

1027.  If,  on  the  other  hand,  the  organ  possesses  little  or  no 
tension,  it  is  conceivable  that  the  growth  would  result  in  a  cur- 
vature of  the  extremity  towards  the  ground  ;  this  is  seen  in  the 
case  of  roots.      The  same  factors  produce  an  upward  curvature 
where  there  is  marked  tension  of  tissues,  and  permit  a  down- 
ward curvature  where  there  is  little  or  no  tension.     It  is  a  sig- 
nificant fact  that  in  the  case  of  certain  branches  from  roots  the 
direction  of  growth  is  oblique. 

1028.  Organs  which  turn  towards  the  earth  are  termed  ffeo- 
tropic;  those  which  turn  upwards  are  apogeotropic  /  those  which 
pursue  in   their  growth  oblique  directions   have   been  termed 
diageotropic. 

1029.  Heliotropism.     It  can  be  shown  by  exact  measurement 
that  in  many  cases  light,  especially  the  more  refrangible  part  of 

FiO.  173.    ViciaFaba.    Descent  of  root  into  mercury.    (Sachs.) 


HELTOTROPISM.  393 

the  spectrum,  has  a  retarding  effect  upon  the  growth  of  certain 
parts,  —  for  instance,  upon  that  of  shoots,  —  exhibiting  itself 
in  the  curvature  of  the  part  towards  the  side  of  greatest  illu- 
mination. Such  curvatures  are  said  to  be  hdiotropic.  It  is, 
however,  well  known  that  the  shoots  and  some  other  parts  of 
a  few  plants  turn  away  from  the  light  ;  such  are  termed 
apheliotropic.1 

1030.  Little  is  known  positively  as  to  the  nature  of  the  influ- 
ence which  light  exerts  upon  growth.     The  studies  of  Vines 
have  shown  that  the  influence  is  largely  due  to  the  modification 
of  the  turgescence  of  growing  cells.     ' '  The  conditions  of  growing 
and  of  contractile  cells  are  in  some  respects  the  same.    Turgidity 
is  essential  to  the  proper  fulfilment  of  the  functions  of  both,  and 
it  has  been  shown  that  light  has  the  power  of  inhibiting,  more  or 
less  completely,  the  activity  of  both.     The  most  general  case  of 
the  action  of  light  upon  growing  cells  has  been  shown  .to  be  a 
diminution  in  the  rapidity  of  their  growth.     The  cell  with  dimin- 
ished or  arrested  growth  may  be  fairty  compared  with  one  of  the 
cells  of  a  rigid  motile  organ.     In  both,  the  micellae  of  the  pro- 
toplasm are  in  a  state  of  stable  equilibrium  so  that  they  do  not 
yield,  in  the  former  case  to  the  force  which  tends  to  separate 
them,  namely,  the  pressure  of  the  cell  contents,  and  in  the  latter 
to  the  force  which  tends  to  bring  them  nearer  together.     The 
theory  that  the  action  of  light  upon  growing  cells  and  upon  those 
of  motile  organs  is  due  to  such  a  modification  of  the  relations 
existing  between  the  micellae  of  the  protoplasm  that  the  mobility 
of  the  micellae  is  diminished,  thus  gives  a  satisfactory  explana- 
tion of  many  phenomena  which  at  first  sight  seem  not  to  have 
much  in  common."  2 

1031.  Hydrotropism.     It  has  been  shown  by  several  experi- 
menters  that  rootlets   when   developing   in  moist   air   deviate 
towards  a  moist  surface.     This  phenomenon,  which   has  been 
examined  in  detail  by  Sachs,   is  termed  Hydrotropism.     The 


1  In  order  to  examine  the  effects  of  the  different  parts  of  the  spectrum  upon 
the  growth  and  movements  of  plants,  the  student  should  cultivate  in  cases  of 
glass  of  different  colors  two  or  three  seedlings,  as  many  bulbous  plants,  and 
some  well-rooted  cuttings  of  hardy  house-plants,  for  instance  Pelargonium. 
Observe  whether  the  growth  is  more  or  less  rapid  under  blue  glass,  and  note 
whether  all  the  seedlings  circumnutate  in  the  same  manner  in  the  different 
eases.     It  should  be  borne  in  mind  that  the  bulbous  plant  as  it  starts  has  a 
generous  supply  of  available  food,  whereas  the  seedling  has  a  more  scanty  store, 
and  the  cutting  very  little. 

2  Arbeiten  des  bot.  Inst.  in  "Wurzburg,  1878,  p.  147. 


394  VEGETABLE   GROWTH. 

accompanying  figure  shows  an  easy  method  of  demonstrating 
this  mode  of  governing  the  direction  of  growing  roots. 


1032.  Thermotropism.     As  might  be  expected  from  what  has 
been  said  regarding  the  tensions  of  tissues  and  the  facility  with 
which  their  balance  is  disturbed,  the  effect  of  warmth  in  govern- 
ing the  direction  of  a  growing  organ  must  be  considerable.    Cur- 
vatures dependent  upon  temperature  are  called  thermotropic. 

1033.  Assumption  of  definite  form  during  growth  depends,  of 
course,  chiefly  upon  inherited  tendencies ;  but  there  have  been 
experiments  which  show  that  to  a  slight  extent  it  may  be  pos- 
sible by  external  influences  to  induce  special  shapes  of  growing 
structures.     Among  the  most  interesting  of  these  are  the  experi- 
ments by  Pfeffer l  upon  the  growth  of  bilateral  organs  in  some 
of  the  lower  plants,  especially  Marchantia ;  by  De  Vries 2  upon 


1  Arbeiten  des  hot.  Inst.  in  Wiirzburg,  1871,  p.  77. 

2  Arbeiten  des  bot.  Inst.  in  Wiirzburg,  1872,  p.  223. 

PIG.  174.  Boots  of  seedlings  affected  by  moisture  during  their  descent.  The  ap- 
paratus consists  of  a  network  frame  filled,  with  moist  sawdust  in  which  the  seedlings 
germinate.  (Sachs.) 


FORCE    EXERTED   DURING    GROWTH.  395 

bilateral   symmetry ;    by  Vochting 1  upon   the   modification    of 
foliar  and  axial  organs. 

1034.  The  amount  of  force  which  is  exerted  by  certain  organs 
during  their  growth  has  been  accurately  measured  for  only  a  few 
cases.     Thus  Darwin  2  found  that  the  transverse  growth  of  the 
radicle  of  a  germinating  bean  was  able  to  displace  a  weight  of 
1,500  grams,  or  3  Ibs.  4  oz.,  and  in  another  instance,  8  Ibs.  8  oz. 
k'  With  these  facts  before  us,  there  seems  little  difficulty  in  under- 
standing how  a  radicle   penetrates  the  ground.     The  apex  is 
pointed,  and  is  protected  by  the  root-cap  ;  the  terminal  growing 
point  is  rigid,  and  increases  in  length  with  a  force  equal,  as  far 
as  our  observations  can  be  trusted,  to  the  pressure  of  at  least  a 
quarter  of  a  pound,  probably  with  a  much  greater  force  when 
prevented  from  bending  to  any  side  by  the  surrounding  earth. 
Whilst  thus  increasing  in  length  it  increases  in  thickness,  push- 
ing away  the  damp  earth  on  all  sides,  with  a  force  of  above 
eight  pounds  in   one  case,  of  three  pounds  in  another  case. 
.  .   .  The  growing  part  does  not  therefore  act  like  a  nail  when 
hammered  into  a  board,  but  more  like  a  wedge  of  wood,  which, 
whilst  slowly  driven  into  a  crevice,  continually  expands  at  the 
same  time  by  the  absorption  of  water ;  and  a  wedge  thus  acting 
will  split  even  a  mass  of  rock." 

By  means  of  a  framework  placed  around  the  fruit  of  a  vigor- 
ous squash  kept  under  conditions  most  favorable  to  its  rapid 
development,  Clark 8  estimated  the  force  exerted  by  growth  to 
be  about  5,000  pounds. 

1035.  That  external  pressure  can  retard  growth  is  well  shown 
by  the  experiments  of  De  Vries 4  upon  the  formation  of  autumn 
wood  (see  page  138).     By  increasing  the  external  pressure  ex- 
erted by  the  bark  he  was  able  to  diminish  the  calibre  of  the 
wood-cells  and  ducts  ;  whereas,  by  diminishing  the  pressure  (by 
making   longitudinal   incisions  into  the  bark)  he  was  able  to 

1  Botanische  Zeitung,  1880,  p.  593. 

2  The  Power  of  Movement  in  Plants,  1881,  p.  76. 

3  For  a  full  account  of  this  experiment,  see  Report  of  the  Secretary  of  the 
Massachusetts  Board  of  Agriculture  for  1874. 

The  great  force  exerted  by  the  increase  in  size  of  the  stems  and  roots  of 
woody  plants  is  sometimes  demonstrated  in  an  extraordinary  manner  by  the 
development  of  seedlings  in  crevices.  Thus,  at  the  Marien  Cemetery  in 
Hanover,  Germany,  the  base  of  a  tree  has  dislodged  the  heavy  stones  of  a 
strongly  built  tomb.  One  of  the  stones,  which  measures  23  X  28  X  56  inches, 
has  been  lifted  upon  one  side  to  the  height  of  five  inches.  The  tree  measures 
just  above  its  base  from  ten  to  fourteen  inches  in  diameter. 

*  Flora,  1872,  p.  241. 


396  VEGETABLE   GROWTH. 

cause  a  considerable  enlargement  of  the  similar  elements.  Fur- 
ther observations  led  him  to  the  conclusion  that  the  striking 
differences  between  spring  and  autumn  wood,  upon  which  the 
annual  rings  depend,  are  due  to  the  greater  pressure  which  is 
exerted  by  the  bark  in  the  latter  part  of  the  summer. 


CHAPTER  XIII. 

MOVEMENTS. 

1036.  MOST  of  the  movements  exhibited  by  plants  are  asso- 
ciated with  growth.      In  the  preceding  chapter  attention  has 
been  called  to  some  of  these  movements,  especially  those  which 
are   characterized   by   a   change   in   the   direction   of  growing 
parts   (see  Gcotropism,   Heliotropism,   etc.).      In   the   present 
chapter  it  is   proposed  to  examine   continuous  and   recurrent 
movements,  and  indicate  to  what  extent  these  are  likewise  the 
accompaniment  of  growth. 

In  the  existing  state  of  knowledge  no  satisfactory  classifica- 
tion of  the  movements  of  plants  can  be  made.  The  provisional 
one  now  to  be  followed  is  adopted  only  for  convenience. 

1037.  Locomotion,  or  movement  of  the  whole  organism  from 
place  to  place,  can  be  observed  in  some  of  the  lower  plants. 
One  of  the  most  interesting  examples  is  furnished  by  ^Kthalium 
septicum,  which  at  certain  stages  of  its  existence  consists  of 
approximately  pure  protoplasm  in  a  naked  state.     Under  favor- 
able conditions  this  naked  mass   (the  plasmodium),  which  fre- 
quently attains  considerable  size,  passes  in  a  creeping  manner 
over  a  moist  surface,  thrusting  out  processes  in  an  apparently 
irregular  manner,  sometimes  retracting  them,  but  more  often 
bringing  up  to  the  advanced  part  the  rest  of  the  uneven  mass. 

The  sensitiveness  of  this  mass  to  the  action  of  external  influ- 
ences renders  it  a  suitable  object  for  the  examination  of  the 
essential  properties  of  protoplasm,  and  man}*  of  the  more  im- 
portant facts  relative  to  its  movement  have  therefore  already 
been  given  (see  550).  It  is  important  to  notice  particularly  that 
there  is  a  rhythmical  pulsation  of  the  sap-cavities  or  vacuoles  in 
the  plasmodium,  dependent,  it  is  supposed,  upon  the  irregular 
absorption  of  water  with  a  varying  imbibition  power.  This  spon- 
taneous pulsation  is  somewhat  affected  by  external  conditions ; 
for  instance,  it  is  increased  in  rate  by  heat  and  diminished  by 
cold. 

1038.  Portions  of  protoplasmic  matter  concerned  in  the  repro- 
duction of  many  of  the  lower  plants,   especially  those  which 


398 


MOVEMENTS. 


live  wholly  in  the  water,  as  the  algae,  have  the  power  of  inde- 
pendent locomotion.  This  is  exhibited  strikingly  in  the  motile 
spores,  which  are  provided  with  cilia,  and  can  thereby  propel 
themselves  from  place  to  place  with  considerable  rapidity.  Sim- 
ilar independent  motion  is  shown  also  by  the  antherozoids  of 
many  of  the  lower  and  even  some  of  the  higher  cryptogams. 

The  protoplasmic  movement  by  which  such  locomotion  is 
secured  is  essentially  identical  with  certain  ciliary  movements 
observed  in  the  animal  kingdom. 

1039.  It  is  a  familiar  fact  that  some  minute  algae,  furnished 
either  with  walls  of  cellulose  (Desmids)  or  cellulose  impregnated 
with  silicic  acid  (Diatoms),  possess  the  power  of  motion,  but 
the  cause  is  not  well  understood.  In  the  case  of  the  skiff-shaped 
diatom  the  motion  is  somewhat  spasmodic,  and  the  course  of 
the  organism  through  the  water  is  not  in  a  straight  line,  but  it 
is  nevertheless  enabled  to  traverse  a  considerable  distance  in  a 
short  time.  Owing  to  the  absence  of  any  distinct  cilia,  it  is 
difficult  to  conceive  the  mechanism  of  propulsion.  According  to 
Max  Schultze  there  is  a  minute  slit  on 
the  under  side  of  the  motile  diatoms,  and 
through  this  slit  a  delicate  film  of  proto- 
plasmic matter  projects.  By  contact  of 
this  motile  film  with  surrounding  objects, 
the  diatom,  as  it  is  supported  in  the 
water,  is  transported  from  place  to  place. 
These  three  cases  of  locomotion,  name- 
ly, of  (1)  naked  protoplasm,  (2)  of  ciliated 
structures,  (3)  of  apparently  closed  cells, 
do  not  exhaust  the  list  of  instances  of 
motion  of  vegetable  organisms  from  place 
to  place ;  other  cases  are  referred  to  the 
succeeding  volume  upon  the  lower  plants. 
1040.  The  movement  of  protoplasm  with- 
in cell- walls  has  already  been  sufficiently 
examined  (see  546)  ;  but  attention  should 
now  be  called  to  the  fact  that  chlorophyll 
granules  (which  are  always  embedded  in 
the  protoplasmic  mass)  frequently  assume 
at  night,  or  when  a  portion  of  the  leaf  is 
darkened,  positions  different  from  those 
which  they  have  during  strong  exposure  to  light.  This  change 


FIG.  175.    Circulation  of  protoplasm  in  hair  of  Gourd.    (Sachs.) 


HYGROSCOPIC    MOVEMENTS. 


399 


of  position  is  well  observed  in  the  thin  leaves  of  some  mosses,  the 
grains  generally  (1)  gathering  on  the  side  walls  under  bright  light, 
but  (2)  occupying  the  upper  and  lower  faces  of  the  cells  when 
the  intensity  of  the  light  is  much  diminished.  The  first  mode 
of  arrangement  is  termed  apostrophe,  the  second  epistrophe.1 

1041.  Hygroscopic  movements  are  dependent  upon  the  property 
possessed  by  dry  vegetable  tissues  of  swelling  more  or  less  under 
the  influence  of  moisture.  They  are  most  strikingly  exhibited  in 
the  case  of  simple  parts,  like  the  filamentous  appendages  of  the 
spores  of  Equisetum  and  the  teeth  of  the  peristome  of  certain 
mosses,  notably  that  of  Funaria  hygrometrica.  They  are  also 
seen  in  the  long  appendages  of 
man}7  fruits ;  for  example,  in 
the  awns  of  some  grasses,  in 
some  Geraniaceae,  etc.,  where 
the}"  serve  the  useful  purpose  of 
fastening  the  fruit  with  its  en- 
closed seed  in  favorable  soil. 
When  the  fruit  falls  upon  moist 
soil,  it  at  first  lies  flat;  later, 
the  extremit}*  of  the  appendage 
and  the  tip  of  the  fruit  form 
fixed  points  in  the  ground  ;  and 
then,  as  moisture  is  absorbed 
by  the  dry  tissue,  a  spiral  curva- 
ture throughout  the  whole  takes 
place.  This  continues  to  twist 
the  tip  of  the  fruit  down  into 
the  soil,  much  after  the  fashion 
of  a  corkscrew.  This  kind  of  movement  is  most  surprisingly 
shown  in  some  of  the  grasses  of  South  America,  and  in  our 
native  Stipa. 

In  not  a  few  instances  the  whole  plant  becomes  relatively  dry, 
rolling  up  into  a  roundish  mass  which  becomes  expanded  again 
upon  access  of  water.  Good  examples  of  such  action  are  afforded 


1  In  some  cases  the  aggregation  of  the  chlorophyll  granules  differs  somewhat 
from  that  described  in  the  text.  For  a  discussion  of  this  subject,  consult 
Frank  (Botanische  Zeitung,  1871,  and  Pringsheim's  Jahrbucher,  viii.,  1872), 
also  Stahl  (Botanische  Zeitung,  1880).  Sachs,  Prillieux,  and  Famintzin  have 
contributed  much  to  the  discussion. 

FIG.  176.  Cross-section  through  the  leaf  of  Lemna  triscula,  showing  the  position  of 
the  chlorophyll  granules:  A,  during  the  day ;  B,  during  exposure  to  strong  light ;  C, 
during  the  night.  (Stahl.) 


400  MOVEMENTS. 

by  the  so-called  Resurrection  plant  of  California  (Selaginella  lepi- 
dophylla) ,  and  by  the  Oriental  plant  known  as  the  Rose  of  Jericho. 
The  latter  plant,  when  dry  and  shrunken  into  small  compass, 
takes  the  shape  of  an  irregular  ball,  becomes  detached  from  the 
ground  where  it  has  grown,  and  may  be  blown  about  over  great 
distances  ;  if  it  has  ripe  seeds,  these  are  scattered  during  transit. 

1042.  Movements  due  to  changes  in  structure  daring  ripening 
of  fruits.      The  fruit  of  the  common  Impatiens,  or  Touch-me- 
not,  affords  a  familiar  instance  of  the  movements  of  this  class. 
As  it  approaches  maturity,  the  valves  of  the  capsule  become 
tense,  each  one,  so  to  speak,  holding  the  others  in  place ;  and 
when  they  are  disturbed  by  even  a  slight  touch  they  separate 
violently,  and  by  their  spring  throw  the  seeds  to  considerable 
distances.      In  some  cases  the  mechanism  is  more  elaborate, 
notably  in  the  cucumber-like  fruit  of  MomordicaElaterium.     In 
this  the  separation  of  the  fruit-stalk  permits  a  sudden  shrinking 
of  the  whole  pericarp  and  a  violent  escape  of  the  seeds  with  a 
viscid  liquid  through  the  opening  made  by  the  separation.     The 
seeds  are  projected  considerable  distances  from  the  fruit. 

Hildebrand l  distinguishes  between  (1)  dry  explosive  fruits 
(such  as  Violet,  Witch-Hazel,  and  Lupinus  luteus),  and  (2) 
fleshy  explosive  fruits  (such  as  Impatiens,  Momordica,  and 
Cardamine  hirsuta) . 

1043.  Revolving  movements,  or  Circnmnntation.    The  tips  of  all 
young  growing  parts  of  the  higher  plants,  as  well  as  the  tips  of 
mam1  of  the  lower,  revolve  through  some  orbit,  either  a  circle  or 
some  form  of  the  ellipse,  the  latter  sometimes  being  so  narrow 
that  it  becomes  practically  a  straight  line.      During  its  revo- 
lution  a  tip  bows   or   nods  successively  to   all   points  of  the 
compass ;    whence  the  name  nutation,  or,  as  termed  by  Sachs, 
revolving  nutation.    Darwin,  who  re-examined  the  whole  subject, 
has  suggested  a  more  general  term,  namely,  circumnutation. 

"  Circumnutation  depends  on  one  side  of  an  organ  growing 
quickest  (probably  preceded  by  increased  turgescence) ,  and 
then  another  side,  generally  almost  the  opposite  one,  growing 
quickest."  2 

1044.  Owing  to  the  fact  that  there  are  numerous  instances  in 
which  the  revolving  movements  are  variously  modified,  that  is, 
"  a  movement  already  in  progress  is  temporarilj-  increased  in 


1  Pringsheim's  Jahrbiicher,  ix.,   1873,   p.  235,  where  the  whole  subject  is 
discussed  in  an  interesting  manner. 

2  Darwin  :  Power  of  Movement  in  Plants,  1880,  p.  99. 


CIRCUMNUTATION. 


401 


some  one  direction  and  temporarily  diminished  or  arrested  in 
other  directions,"  it  has  been  found  convenient  to  discriminate 
between  circumnutation  and  modified  circumnutation.  Darwin 
divides  the  latter  into  two  classes  of  movements :  (1)  those 
dependent  on  innate  or  constitutional  causes,  and  independent 
of  external  conditions,  except  that  the  proper  ones  for  growth 
must  be  present ;  (2)  those  in  which  the  modification  depends 
to  a  large  extent  on  external  agencies,  such  as  the  daily  alter- 
nations of  light  and  darkness,  light  alone,  temperature,  or  the 
action  of  gravity.  It  is  plain  that  such  a  division  cannot  be  ab- 
solute ;  in  fact,  numerous  intermediate  cases  are  known  to  exist. 


1045.  Methods  of  observation  of  circumnutation.  For  meas- 
uring the  rate  and  determining  the  exact  direction  of  the  move- 
ments of  circumnutating  parts  when  the  parts  are  small  and 
the  movements  slight,  the  following  methods  described  by  Dar- 
win l  can  be  employed  in  nearly  all  cases  where  it  is  necessary 
to  magnify  the  amount  of  displacement. 

1  Power  of  Movement  in  Plants,  1880,  p.  6. 

Fio.  177.  Angular  movements  of  a  leaflet  of  Averrhoa  bilimbi  during  its  evening 
descent,  when  going  to  sleep.  Temp.  78-81°  F.  The  ordinates  represent  the  angles 
which  the  leaflet  made  with  the  vertical  at  successive  instants.  A  fall  in  the  curve 
represents  an  actual  dropping  of  the  leaf,  and  the  zero  line  represents  a  vertically 
dependent  position.  Each  oscillation  consists  of  a  gradual  rise  followed  by  a  sudden 
fall.  (Darwin.) 


402 


MOVEMENTS. 


A  very  slender  filament  of  glass,  made  by  drawing  out  a  thin 
glass  tube  until  it  is  no  larger  than  a  hair,  is  to  be  affixed  to  the 
tip  of  the  root,  stem,  or  leaf  under  observation  ;  this  is  easily 
done  by  means  of  a  quickly  drying  varnish,  for  instance  shellac 
dissolved  in  alcohol.  In  order  to  mark  the  path  made  by  the 
filament  it  is  best  to  cement  to  the  tip  of  the  slender  hair  of 
glass  a  very  minute  bead  of  black  sealing-wax,  "behind  which 
a  bit  of  card  with  a  black  dot  is  fixed  to  a  stick  driven  into  the 
ground.  The  bead  and  the  dot  on  the  card  are  viewed  through 
the  horizontal  or  vertical  glass  plate  (according  to  the  position  of 
the  object),  and  when  one  exactly  covers  the  other,  a  dot  is  made 
on  the  glass  plate  with  a  sharply  pointed  stick  dipped  in  thick  In- 
dia ink.  Other  dots 
are  made  at  short 
intervals  of  time, 
and  these  afterwards 
joined  by  straight 
lines.  The  figures 
thus  traced  are  an- 
gular ;  but  if  the 
dots  are  made  every 
one  or  two  minutes 
the  lines  are  more 
curvilinear,  as  oc- 
curs when  radicles 
are  allowed  to  trace 
their  own  course  on 
smoked  glass  plates." 
"  Whenever  a 
great  increase  of  the 
movement  is  not  re- 
quired, another  and  in  some  respects  a  better  method  of  obser- 
vation is  followed.  This  consists  in  fixing  two  minute  triangles 
of  thin  paper,  about  one  twentieth  of  an  inch  in  height,  to  the 
two  ends  of  the  attached  glass  filament ;  and  when  their  tips  are 
brought  into  a  line  so  that  they  cover  one  another,  dots  are  made 
as  before  on  the  glass  plate."1 

1  It  is  very  convenient  to  employ  large  bell-jars,  or  hemispherical  glasses, 
as  glass  screens  upon  which  to  record  the  dots  indicating  the  position  of  the 
tip  at  any  given  moment.  It  must  be  remembered  that  in  all  these  cases  there 

Fro.  178.  Tracing,  showing  the  conjoint  circumnutation  of  the  liypocotyl  and  cotyle- 
dons of  Brassica  oleracea  during  10  hours  and  46  minutes.  Figure  reduced  to  one  half 
original  scale.  (Darwin.) 


CIKCUMNUTATION    IN    SEEDLINGS.  403 

1046.  Circumnutatiou  in  seedlings.    That  part  of  the  axis  which 
is  below  the  cotyledons  is  made  up  of  a  rudimentary  stem  known 
as  the  caulicle  or  hypocotyl,  and  a  rudimentary  root  or  radicle 
proper.     The  part  of  the  young  stemlet  above  the  cotyledons  is 
termed  the  epicotyl.     In  the  cotyledons  of  the  plantlet,  when 
freed  from  the  seed-coats,  and  in  all  parts  of  the  young  axis, 
slight  movements  can  be  observed.      In  all  observations  it  is 
necessary  to  remove  the  plantlet  as  far  as  possible  from  disturb- 
ing conditions  ;  thus,  all  light  must  be  excluded  until  the  moment 
of  making  the  observation,  when  only  a  faint  light  should  be 
employed. 

1047.  Two  facts  are  easily  apparent  with  regard  to  the  revolv- 
ing radicle:  (1)  its  extreme  sensitiveness  to  contact ;  (2)  its  ten- 
dency to  yield  to  geotropism  (see  1026). 

1048.  The  caulicle,  upon  emerging  from  the  seed-coats,  is 
often  more  or  less  arched ;  but  it  may  become  straight  after  a 
short  time,  when  it  can  be  seen  to  pass  through  an  elliptical  orbit 
by  which  the  plane  of  the  cotyledons  is  somewhat  inclined  suc- 
cessivety  to  all  points  of  the  compass.     Darwin  has  shown  that 
even  before  the  liberation  of  the  caulicle  from  the  seed-coats,  when 
both  columns  of  the  arch  are  held  in  the  soil,  the  top  of  the  arch 
moves  with  considerable  regularity.     It  is  difficult  to  understand 
how  the  summit  of  the  arch  formed  by  the  curved  caulicle  can 
revolve  when  both  of  its  supporting  columns  are  fixed  in  the  soil. 
Darwin   has   accepted   an   explanation   suggested   b}-  Wiesner, 
which  is  briefly  as  follows :    In  a  given  internode  (it  must  be 
remembered  that  the  caulicle  represents  the  first  internode  of 
the  seedling,  as  shown  in  Volume  I.  page  9)  there  may  be  a  zone 
in  which  the  growth  is  equal  on  all  sides,   and  which   may  be 
termed  the  zone  of  indifferent  growth,  while  on  each  side  of  this 
there  may  be  two  others  in  which  there  is  unequal  growth  at 
intervals  of  time.     Then  by  the  faster  growth  on  one  side  of  the 
arch  the  summit  would  be  thrown  to  one  side,  and  this  process 


is  more  or  less  distortion  produced  by  the  best  methods  of  projection,  and  in 
all  accurate  observations  this  must  be  taken  into  account. 

When  seedlings  are  inverted  so  that  the  glass  filament  is  held  upwards,  it 
must  be  noted  that  the  influence  of  gravitation  must  come  in  as  a  modifying 
element.  To  mark  the  amount  of  influence  exerted  by  gravitation,  it  is  well 
to  vary  the  length  and  weight  of  the  filament  employed.  But  it  must  be  ob- 
served that  the  weight  of  the  organ  itself  is  the  most  important  element  in  the 
problem.  Moreover,  it  has  been  observed  that  all  young  growing  parts,  espe- 
cially the  extremity  of  the  radicle,  are  more  or  less  sensitive  ;  and  hence  the 
course  of  the  filament  may  be  somewhat  modified  by  even  slight  contact, 


404  MOVEMENTS. 

would  sooner  or  later  be  succeeded  by  its  reversal ;  and  thus  the 
summit  would  be  made  to  circumnutate. 

1049.  Darwin's1  illustration  of  the  movements  of  the  parts  of 
seedlings  gives  a  clear  idea  of  their  sequence.     "  A  man  thrown 
down  on  his  hands  and  knees  and  at  the  same  time  to  one  side 
by  a  load  of  hay  falling  on  him,  would  first  endeavor  to  get  his 
arched  back  upright,  wriggling  at  the  same  time  in  all  directions 
to  free  himself  a  little  from  the  surrounding  pressure ;  and  this 
may  represent  the  combined  effects  of  apogeotropism  and  cir- 
cumnutation  when  a  seed  is  so  buried  that  the  arched  hypocotyl 
or  epicotyl  protrudes  at  first  in  a  horizontal  or  inclined  plane. 
The  man,  still  wriggling,  would  then  raise  his  arched  back  as 
high  as  he  could  ;  and  this  may  represent  the  growth  and  con- 
tinued circumnutation  of  an  arched  hypocotyl  or  epicotyl  before 
it  has  reached  the  surface  of  the  ground.     As  soon  as  the  man 
felt  himself  at  all  free,  he  would  raise  the  upper  part  of  his  body, 
whilst  still  on  his  knees  and  still  wriggling ;  and  this  may  repre- 
sent the  bowing  backwards  of  the  basal  leg  of  the  arch,  which  in 
most  cases  aids  in  the  withdrawal  of  the  cotyledons  from  the 
buried  and  ruptured  seed-coats,   and  the  subsequent  straight- 
ening of  the  whole  hypocotyl  or  epicotyl,  circumnutation  still 
continuing." 

1050.  The  cotyledons  not  only  share  the  movement  of  the 
caulicle,  but  they  have  also  an  independent  movement  which 
is  greatly  modified  by  slight  changes  in  the  surroundings.    Freed 
from  their  seed-coats,  they  move  upwards  and  downwards  in  very 
narrow  ellipses,  and  at  different  rates  in  different  plants.     Gen- 
erally their  movement  takes  place  only  once  in  the  course  of  the 
twenty-four  hours :  in  Cassia  tora,  on  an  average,  once  in  about 
two  hours  ;  in  Oxalis  rosea,  once  in  about  three  hours  ;  while  in 
Ipomoea  coerulea  Darwin  observed  the  change  of  position  to  occur 
almost  hourly.     It  is  noticeable  that  the  cotyledons  may  change 
the  direction  of  their  movement  slightly  at  different  times  of  the 
day,  and  may  thus  have  a  zigzag  course  during  a  part  of  the  day 
and  a  nearly  regular  orbit  during  the  rest. 

1051.  In  some  of  the  seedlings  which  have  been  examined  with 
especial  reference  to  their  movements  there  is  a  joint  or  swelling 
to  be  detected  at  the  base  of  the  petiole.     This  is  the  equivalent 
of  the  pulvinus  commonly  found  in  Sensitive  plants ;  changes  in 
the  position  of  cotyledons  provided  with  such  joints  depend,  as 
in  the  case  of  sensitive  leaves,  upon  variations  in  the  turgescence 

1  Power  of  Movement  in  Plants,  1880,  p.  106, 


TWINING   PLANTS. 


405 


of  the  cells  composing  it,  while  changes  in  the  position  of  cotyle- 
dons devoid  of  them  are  due  to  unequal  growth. 

1052.  Circnmnutation  of  the  yonng  parts  of  mature  plants.     By 
methods  similar  to  those  described  in  1045,  it  can  be  shown  that 
the  growing  extremities  of  stems,  branches,  leaves,  and  their 
numerous   modifications  possess  the   power  of  movement;    in 
some  instances  exhibiting  essentially  the  same  phenomena  as 
those  presented  by  the  parts  of  the  seedling,  while  in  other  cases 
they  show  differences  at  an  early  stage.     The  most  striking  of 
these  differences  is  that  observed  in  twining  stems.    In  this  case 
there  is  a  greatly  increased  amplitude  of  the  orbit  through  which 
the  tip  of  the  stem  passes.     Although  only  a  special  case  under 
a  general  class,  twining  stems  may  well  receive  a  somewhat 
detailed  description. 

1053.  Twiners  are  distinguished  from  proper  climbers  by  the 
absence  of  any  special  organs,  other  than  the  stem  itself,  for 

grasping  sup- 
ports ;  climbers 
being  provided 
with  some  sort 
of  tendrils,  or 

other  help,  by  which  the  plant  is  held  to  its  sur- 
roundings. Taking  the  simplest  cases  of  twiners, 
such  as  that  of  the  common  Morning  Glory,  it  is 
to  be  observed  that  (1)  the  revolving  movement 
begins  at  the  earliest  moment;  (2)  only  a  few 
j-oung  internodes  are  concerned  in  the  revolving ; 
(3)  the  revolving  stem  cannot  twine  around  a 
smooth  support  (for  example,  a  glass  rod),  but 
requires  in  the  support  some  degree  of  rough- 
ness ;  (4)  there  is  a  limit  of  size  to  the  support, 
different  for  different  twiners.  be3Tond  which  it 
cannot  be  grasped  by  the  revolving  stem  ;  (5) 
the  direction  of  the  revolution  is  not  the  same  for  all  twiners ; 
(6)  the  rate  differs  with  the  plant  and  with  the  surroundings. 

1054.  In  the  early  state  of  a  twining  plant  the  movements  are 
in  narrow  ellipses  ;  but  with  even  a  slight  increase  in  size  of  the 
seedling,  the  transverse  axis  of  the  ellipse  becomes  greater,  and 
soon  the  orbit  is  practical!}-  a  circle. 

1055.  The  number  of  internodes  concerned  in  the  twining 
movement  is  usuallj"  not  more  than  three  or  four,  and  sometimes 


FIG.  179.    Involving  shoot  of  Morning  Glory. 


406  MOVEMENTS. 

only  two  are  involved.  The  iuternodes  below  the  seat  of  move- 
ment are  rigid.  The  revolving  is  associated  with  growth,  but 
the  growth  alone  is  probably  not  the  sole  cause  of  the  move- 
ment. 

1056.  It  is  only  the  young  internodes  which  are  capable  of 
spontaneous  movement ;    but  growth  itself,   unassociated   with 
changes  in  the  turgescence  of  the  tissues  upon  the  different  sides, 
would  not  be  sufficient  to  account  for  the  movement.     It  must 
be  remembered  that  the  young  stem  possesses  remarkable  ten- 
sions, which  are  easily  disturbed  by  slight  internal  as  well  as 
external  causes.    The  increased  turgescence  of  its  cells  upon  one 
side,  or  their  diminished  turgescence  on  the  other,  or  the  action 
of  both  conjointly,  followed  as  this  is  by  an  increased  growth  of 
the  turgescent  part,  would  produce  sufficient  change  in  the  cur- 
vature of  the  stem  to  bring  about  the  twining  movement. 

1057.  When  a  twining  stem  comes  in  contact  with  a  smooth 
support,  it  generally  slides  up  the  support,  but  fails  to  grasp  it. 
The  check  which  is  given  by  a  smooth  support  sometimes  brings 
about  a  change  of  position  in  the  revolving  stem,  which  is  thus 
described  by  Darwin:  "When  a  tall  stick  was  so  placed  as  to 
arrest  the  lower  and  rigid  internodes  of  Ceropegia,  at  the  dis- 
tance at  first  of  fifteen  and  then  of  twenty-one  inches  from  the 
centre  of  revolution,  the  straight  shoot  slowly  and  gradually  slid 
up  the  stick,  so  as  to  become  more  and  more  highly  inclined, 
but  did  not  pass  over  the  summit.     Then  after  an  interval  suffi- 
cient to  have  allowed  of  a  semi-revolution,  the  shoot  suddenly 
bounded  from  the  stick,  and  fell  over  to  the  opposite  side  or 
point  of  the  compass,  and  reassumed  its  previous  slight  inclina- 
tion.    It  now  recommenced  revolving  in  its  usual  course,  so  that 
after  a  semi-revolution  it  again  came  in  contact  with  the  stick, 
again  slid  up  it,  and  again  bounded  from  it  and  fell  over  to  the 
opposite  side.     This  movement  of  the  shoot  had  a  very  odd  ap- 
pearance, as  if  it  were  disgusted  with  its  failure,  but  was  resolved 
to  try  again." l 

1058.  Many  of  the  common  twiners  of  temperate  climates  are 
able  to  twine  round  very  slender  supports,  for  instance  a  small 
cord,  but  are  unable  to  twine  round  a  post  or  trunk  of  a  tree. 
This  does  not,  however,  appear  to  be  wholly  dependent  upon  the 
amplitude  of  the  revolution.     In  tropical  regions  some  of  the 
twiners  ascend  trunks  of  immense  size,  but  they  are  generally 
assisted  by  adventitious  roots,  etc. 

*  Climbing  Plants,  1875,  p.  21, 


MODIFIED  CIRCUMNUTATION.  407 

1059.  An}'   given   twiner  generally  twines  in  one  direction 
only ;  for  instance,  the  hop  moves  in  the  direction  of  the  hands 
of  a  watch,  or  to  use  another  expression,  follows  the  sun  ;  the 
Morning  Glory  moves  in  an  opposite  direction.     But  there  are 
some  cases  in  which  the  direction  of  twining  is  reversed  even 
during   a   comparatively   short   distance.      In  the  tropics  this 
reversal  is  said  to  be  common.1 

1060.  The  time  required  for  the  revolution  of  a  twiner  varies 
in  different  plants,  and  is  by  no  means  constant  for  the  same 
plant  at  different  stages  of  its  development.     In  the  case  of  the 
Morning  Glory,  the  average  time  required  for  the  revolution  of 
a  thrifty  shoot  under  favorable  conditions  is  about  three  hours. 

1061.  Twiners  are  affected  somewhat  by  the  amount  of  light 
received,  but  the  revolving  goes  on  uninterruptedly  night  and 
day.     The  increase  of  rate  when  a  revolving  shoot  is  approach- 
ing a  window  may  be  equal  to  a  tenth,  or  somewhat  more,  of  the 
whole  period  of  the  revolution.     Such  acceleration  is  very  differ- 
ent for  different  plants. 

1062.  Modified  circnmnntation.     The  effect  of  the  influence  of 
light  in  increasing  the  rate  of  movement  in  a  twiner  is  a  good 
example  of  a  large  class  of  modified  movements.     These  move- 
ments have  already  been  considered  in  the  chapter  on  "Growth," 
under  the  terms  Heliotropism,  Geotropism,  etc.,  but  must  be 
again  referred  to  in  connection  with  the  universal  movement, 
circumnutation.     When  it  is  desirable  to  free  any  circumnu- 
tating  part  from  the  influence  of  a  disturbing  factor,  for  instance 
light,  great  care  must  be  taken  to  avoid  subjecting  it  to  abnor- 
mal conditions  such  as  result  when  a  seedling  is  kept  in  the 
dark   in   order   to   free   it  from   the  influence   of  light  on  its 
movements.     When  so  kept  it  undergoes  changes  of  form  with 
its  blanching,  and  therefore   little  security  is  felt  that  all  its 
behavior  is  normal.      In  the  instance  of  green   plants  which 
demand  light  for  their  health}'  activity  the  removal  of  disturbing 
factors  is  a  task  of  considerable  difficult}7. 

A  part  of  the  difficulty  is  removed  by  the  use  of  some  instru- 
ment by  which  the  plants  can  be  made  to  revolve  slowly  in  a 
given  plane,  thus  exposing  the  different  sides  successively  to 
the  action  of  the  force.  A  simple  form  of  this  appliance  is 

.l  Fritz  Miiller  is  quoted  by  Darwin  as  saying,  that  the  stem  of  Davilla 
twines  indifferently  from  left  to  right  or  from  right  to  left  ;  and  that  he  once 
saw  a  shoot  which  had  ascended  a  tree  about  five  inches  in  diameter  reverse 
its  course. 


408 


MOVEMENTS. 


known  as  the  dinostat.  It  consists  of  a  clock-work  which  car- 
ries a  disc  on  which  can  be  placed  growing  plants :  by  the  revo- 
lution of  this  horizontal  disc  all  parts  are  in  turn  given  the  same 
amount  of  illumination.  If  the  clock-work  is  so  arranged  as  to 
rotate  a  horizontal  shaft  to  which  a  growing  plant  can  be  affixed, 
any  one  part  of  the  plant  will  be  exposed  to  the  influence  of 
gravitation  in  precisely  the  same  manner  and  to  the  same  extent 
as  all  other  parts. 

When  circumnutation  is  plainly  modified  by  unequal  growth, 
striking  disturbances  are  produced  which  have  received  much 


investigation.  Among  these  cases  are  the  changes  of  position 
which  many  peduncles  undergo  during  the  development  of  flow- 
ers and  fruits.  Although  the  extremity  of  the  flower-stalk  passes 
through  its  definite  orbit,  it  is  in  some  instances  so  affected  by 
the  greater  growth  of  the  upper  side  as  to  curve  downwards, 
while  a  similar  excessive  growth  on  the  under  side  will  produce 
an  upward  curvature.  De  Vries,  who  has  given  much  attention 
to  these  phenomena,  has  coined  the  adjectives  epinastic,  denoting 
curvature  from  growth  on  the  upper  side,  and  hyponastic,  that 
from  growth  on  the  under  side  of  an  extending  organ. 

FIG.  180.    Disc  of  a  clinostat  covered  by  a  glass  case  g,  and  bearing  two  Windsor 
beans  with  primary  and  secondary  roots. 


NYCTITBOPIC  MOVEMENTS.  409 

1063.  The  ample  revolving  movement  is  not  confined  to  stems, 
but  is  observed  in  some  modified  branches  and  leaves,  for  ex- 
ample in  certain  ten- 
drils, etc.     A  single 

instance  will  serve  to 
show  the  remarkable 
nature  of  the  move- 
ment in  the  case  of 
the  tendrils  of  Echi- 
nocystis  lobata,  as  de- 
scribed by  Darwin : 1 
"These  are  usually 
inclined  at  about  45° 

1OJ. 

above  the  horizon,  but 

they  stiffen  and  straighten  themselves  so  as  to  stand  upright  in 
a  part  of  their  circular  course  ;  namely,  when  they  approach  and 
have  to  pass  over  the  summit  of  the  shoot  from  which  they  arise. 
If  they  had  not  possessed  and  exercised  this  curious  power,  they 
would  infallibly  have  struck  against  the  summit  of  the  shoot  and 
been  arrested  in  their  course.  As  soon  as  one  of  these  tendrils 

with  its  three  branches  be- 
gins to  stiffen  itself  and  rise 
up  vertical!}-,  the  revolving 
motion  becomes  more  rapid  ; 
and  as  soon  as  it  has  passed 
over  the  point  of  difficulty, 
its  motion  coinciding  with 
that  from  its  own  weight 

causes  it  to  fall  into  its  previously  inclined  position  so  quickly 
that  the  apex  can  be  seen  travelling  like  the  hand  of  a  gigantic 
clock." 

1064.  Nyctitropic,  or  sleep,  movements.     The  foliar  organs  of 
man}-  plants  assume  at  nightfall,  or  just  before,  positions  unlike 
those  which  they  have  maintained  during  the  day.     In  many 
cases  the  drooping  of  the  leaves  at  night  is  suggestive  of  rest, 
and  the  name  given  by  Linnaeus  to  this  group  of  phenomena, 
namely,  "the  sleep  of  plants,"  seems  appropriate.    But  in  numer- 
ous cases  the  nocturnal  position  is  one  of  obvious  constraint, 
and  considerable  force  has  to  be  expended  in  lifting  the  leaf  to 

1  Power  of  Movement  in  Plants,  1880,  p.  266. 

FIG.  181.    Leaf  of  Coronilla  rosea  at  night,    f Darwin.) 

Fm.  182.    Leaf  of  White  Clover.    A,  day  position ;  B,  night  position.    (Darwin.) 


410 


MOVEMENTS. 


the  new  position.     The  diversity  of  positions  can  be  only  imper- 
fectly indicated  by  the  accompanying  illustrations. 

According  to  Pfeffer,  the  sleep-movements  of  leaves  and  of 
cotyledons  depend  upon  increased  growth  on  one  side  of  the 

median  line  of  the 
petiole  and  midrib, 
followed  after  a 
certain  interval  of 
time  by  a  corre- 
sponding growth 
on  the  opposite 
side.  Thus  in 
ordinary  leaves 
which  droop  at 
night  the  depres- 
sion is  produced 
by  a  slightly  in- 
creased growth  on  the  upper  side,  and  the  rise  in  the  morning 
by  a  similar  growth  on  the  under  side.  But  in  the  most  striking 
cases  there  is  a 
distinct  appara- 
tus at  the  base 
of  the  leaf-stalk, 
which  accom- 
plishes the  same 
movement  by 
simple  turges- 
cence  of  the  op- 
posite sides. 

The  apparatus 
consists  of  an 
enlargement 
formed  of  cellu- 
lar tissue  in 
which  there  is 
often  an  appre- 
ciable difference 
between  the 
character  of  the 

cell-walls  on  the  upper  and  under  side  of  the  swelling.     This 
swelling,  known  as  the  pulvinus,  permits  the  movement  to  be 


Fio.  183     Leaflets  of  Averrhoa  bilimbi  at  night.    (Darwin.) 

FIG.  184.    Leaf  of  Acacia  Farnesiana  during  the  day  and  at  night.    (Darwin. ) 


SLEEP-MOVEMENTS. 


411 


continued  long  after  the  movements  in  }Toung  leaves  destitute 
of  such  an  apparatus  have  ceased. 

1065.  The  sleep-movements  of  cotyledons  are  extremely  diverse, 
but  in  general  consist  in  an  elevation  of  the  tips,  bringing  the 
upper  faces  into  proximity,  and  sometimes  into  contact.  It  may 
happen  also  that  one  or  more  of  the  earh'  leaves  developed 
from  the  plumule  approaches  the  elevated  cotyledons.  Dar- 
win has  noted  that  in  some  cases  the  cotyledons  of  plants, 
with  ordinary  leaves  which  exhibit  sleep-movements,  may  not 
change  their  position  at  night,  except  as  they  do  in  simple 
circumnutation. 


185 

1066.  The  utility  of  the  sleep-movements  of  leaves  and  cotyle- 
dons is  believed  to  consist  in  protection  from  too  great  radiation 
during  the  night.  Darwin  has  shown  by  simple  and  conclusive 
experiments  that  in  the  case  of  some  plants  this  change  of  the 
position  of  leaves  at  the  approach  of  a  chilly  night  is  a  matter 
of  life  and  death. 

When  leaves  which  naturally  assume  nyctitropic  positions  are 
pinned  or  otherwise  kept  from  changing  their  position,  and  the 
plant  is  exposed  to  a  temperature  a  little  below  freezing,  under 
a  clear  sky,  into  which  the  radiation  of  heat  must  go  on  rapidly 
from  the  upper  surface  of  the  leaves,  serious  injuries  result,  the 
leaves  becoming  browned  and  even  killed ;  whereas,  leaves  on 


FIG.  185.    Desmodium  gyrans.    A,  position  during  the  day ;  B,  position  at  night. 


412  MOVEMENTS. 

the  same  plant  which  are  allowed  to  take  the  protective  position, 
escape. 

1067.  Sleep-movements  of  floral  organs.    These  are,  in  general, 
dependent,   as  Pfeffer  has  clearly  shown,   upon   the   alternate 
growth  of  the  opposed  surfaces.     For  instance  in  a  crocus,  the 
greater  growth  of  the  inner  surface  of  the  parts  of  the  perianth 
will  bring  about  an  opening  of  the  flower,  whereas  the  greater 
growth  of  the  outer  surface  will  effect  a  closing. 

Pfeffer's  method  of  investigation  is  capable  of  application,  pro- 
vided one  has  a  microscope  which  admits  of  being  held  with  its 
tube  horizontal.  A  perianth  leaf  is  carefully  detached  without 
too  much  violence  from  the  flower,  and  immediately  placed  in  a 
small  tube  containing  water,  so  that  the  expanded  part  may  be 
brought  within  the  field  of  the  microscope.  If  fine  lines  are 
measured  off  upon  its  inner  and  outer  surfaces  in  India  ink, 
their  gradually  increasing  distance  from  each  other  can  be 
watched  to  good  advantage.  It  can  then  be  clearly  seen  that 
when  the  part  curves  outward  it  is  owing  to  an  increased  growth 
upon  the  inner  surface,  and  vice  versa.  That  there  is  an  ante- 
cedent turgescence  is  very  likely,  as  has  been  repeatedly  pointed 
out  by  De  Vries  and  others.  It  is  probable  also  that  in  a  few 
cases  the  opening  and  closing  are  due  to  a  temporary  turges- 
cence unaccompanied  b}'  much  growth. 

Changes  in  illumination  and  in  temperature  are  sufficient  to 
effect  the  alternations  of  growth  and  of  turgescence  in  delicately 
constituted  parts,  where  there  is  a  balanced  tension  existing 
between  the  outer  and  inner  tissues. 

1068.  Times  of  opening  and  closing  in  the  open  air.    Under  the 
ordinary  conditions  of  an  equable  climate  the  times  of  opening 
and  closing  of  the  flowers  of  a  given  plant  do  not  vary  widely. 
Hence  it  is  possible  to  construct  a  floral  clock  which  shall  mark 
the  hours  with  tolerable  regularity.    The  dial  at  Upsala,  Sweden, 
suggested  by  Linnfeus,  and  that  designed  for  Paris  by  De  Can- 
dolle,1  are  approximately  correct ;  but  in  a  climate  having  the 
sharp  and  sudden  differences  of  heat  and  of  moisture   which 
characterize  eastern  North  America  such  floral  clocks  are  not 
successful. 

1  The  following  list  from  De  Candolle's  Physiologic  gives  the  hours  of  the 
opening  of  certain  flowers  in  Paris :  — 

Ipomcea  pnrpurea 2     A.  M. 

Calystegia  sepium 3-4     " 

Matricaria  suaveolens 4-5     " 


THE   TELEGRAPH   PLANT.  413 

1069.  The  Telegraph  plant.  The  most  surprising  instance  of 
rapid  spontaneous  movement  is  that  which  is  exhibited  by  the 
lateral  leaflets  of  Desmodium 
gyrans.  Each  complete  leaf 
of  Desmodium  consists  of  a 
large  terminal  leaflet  and  two 
little  lateral  leaflets.  At 
nightfall  the  terminal  leaflets 
sink  vertically,  and  the  peti- 
oles are  somewhat  raised,  so 
that  the  terminal  leaflets  are 
much  crowded  together  upon 
the  stem  (see  Fig.  185.)  The 
cotyledons  do  not  have  this 
nyctitropic  movement,  but 
the  first  true  leaf  sleeps  just 
as  do  the  older  ones. 

The  lateral  leaflets  do  not 
fall  at  night,  but  at  the  tem- 
perature of  36  to  38°  C.,  or 
even  somewhat  higher,  keep 
up,  night  and  da}',  an  irregu- 
lar jerking  movement,  which 
has  been  compared  to  the 
ticking  of  the  second-hand  of 
a  watch  (or,  formerly,  to  the 
movements  of  the  arms  of  a 
Semaphore  Telegraph).  The  tip.  of  the  moving  leaflet  passes 

Papaver  nudicaule  and  most  Cichoriaceae  ...  5      A.  M. 

Convolvulus  tricolor 5-6     " 

Convolvulus  siculus 6         " 

Species  of  Sonchus  and  Hieracium 6-7     " 

Species  of  Lactuca 7         " 

Anagallis  arvensis 8         " 

Calendula  arvensis 9         " 

Arenaria  rubra 9-10  " 

Mesembryanthemum  nodiflorum 10-11  " 

Ornithogalum  umbellatum 11 

Passiflora  ccerulea 12        M. 

Pyrethrum  corymbosum 2     P.  M. 

Silene  noctiflora 5—6 

(Enothera  biennis 6 

Mirabilis  Jalapa 6-7     ' 

Lychnis  vespertina 7 

Cereus  grandiflorus 7-8     ' 

FIG.  186.    Desmodium  gyrans. 


414  MOVEMENTS. 

through  its  elliptical  orbit  in  a  period  of  from  half  a  minute  to  a 
minute  or  more,  the  time  varying  greatly  according  to  the  ex- 
ternal conditions,  but  being  nearly  uniform  under  uniform  higli 
temperature.  The  lateral  leaflets  move  independently  of  one 
another,  one  sometimes  passing  downwards  while  the  other  is 
ascending,  but  there  is  no  distinct  relation  between  them. 

At  the  base  of  the  terminal  leaflet,  the  base  of  the  lateral  leaf- 
lets, and  the  base  of  the  main  petiole,  are  pulvini,  to  changes 
in  which  the  several  movements  are  due. 

1070.  The  cause  of  autonomic  movements  not  fully  known.     As 
to  the  cause  of  the  periodic  changes  in  turgescence  and  asso- 
ciated growth  which  give  rise  to  "  spontaneous  "  movements,  little 
is  at  present  known.     The  fact  that  in  the  naked  protoplasm  of 
the  plasmodium  of  the  Myxomycetes   the  sap  cavities  exhibit 
a  rhythmical  pulsation  which  is  thought  to  be  dependent  upon 
variations  in  the  imbibition  power  of  the  protoplasm  for  water, 
throws  little  light  upon  the  ultimate  cause  which  underlies  vari- 
able turgescence  in  one  case  and  variable  pulsation  in  the  other. 
Although  variations  in  turgescence  and  associated  growth  are 
everywhere  observable  in  }'oung  and  still  parts  of  plants,  in  some 
instances  similar  phenomena  can  be  observed,  as  we  have  just 
seen,  in   specialized  organs   which   are    no   longer   capable   of 
growth. 

1071 .  DeVries l  calls  attention  to  the  fact  that  organic  acids  or 
their  salts,  as  they  are  formed  in  tissues,  have  a  marked  effect 
upon  the  turgescence  of  the  cells  composing  the  tissue.     If  these 
compounds  were  produced  first  in  the  cells  on  one  side  of  a  shoot 
or  other  motile  organ,  and  then  in  the  cells  next  to  these,  and 
so  on,  the  phenomena  of  circumnutation  would  be  exhibited. 
Its  cause  will  probably  be  found  in  chemical  processes  which 
cause  the  osmotic  power  of  the  cell-contents  to  vary.2 

1072.  Sensitiveness.     Ity  this  is  meant   the  capacit}'  to  react 
against  an  irritation ;  thus,  the  root  is  said  to  be  sensitive  to 
moisture,  some  leaves  to  light,  etc.     But  it  is  usual  to  employ 
the  term  in  a  more  restricted  signification ;  following  Darwin's 
cautious  definition,  "  a  part  or  organ  may  be  called  sensitive, 
when  its  irritation  excites  movement  in  an  adjoining  part."  8   The 
irritant  may  be  shock,  prolonged  contact,  a  light  touch,  or  a 
chemical  agent. 

1  Botanische  Zeitung,  1879,  pp.  830,  847,  and  in  an  independent  communi- 
cation. 

2  Pfeffer  :  Periodischen  Bewegungen  (1875). 

8  Power  of  Movement  in  Plants,  1880,  p.  191. 


SENSITIVENESS   OF  ROOTS.  415 

1073.  It   has   been  shown  (1024)  that  young  shoots  react, 
although  somewhat  sluggishly,  against  mechanical  shock,  their 
change  of  form  or  direction  depending  on  the  character  or  direc- 
tion of  the  blows  received.    In  certain  delicate  tissues,  especially 
those  which  possess  much  simplicity  of  structure,  change  of  form 
and  of  direction  may  be  produced  in  response  to  comparatively 
slight  mechanical  or  chemical  irritation.     It  is  to  these  that  the 
term  sensitive  tissues  is  properly  applied. 

1074.  Sensitiveness  of  roots.     The  tip  of  the  caulicle  is  gen- 
erally sensitive  to  contact  and  to  caustics.     There  are,  however, 
great  differences  in  the  degree  of  sensitiveness ;  in  some  cases 
slight  contact  being  sufficient  to  cause  reaction,  while  in  others 
the  contact  must  be  prolonged  and  accompanied  by  direct  pres- 
sure.    If  the  caulicle  with  its  unformed  root  is  placed  under 
conditions  where  growth  can  take  place  with  great  rapidity,  the 
sensitiveness  is  much  impaired  and  sometimes  is  wholly  lost ; 
it  is  partially  lost  also  when  the  caulicle  grows  slowly,   or  is 
forced  to  grow  out  of  season.     Under  natural  conditions  and  at 
a  normal  rate  of  growth  the  tip  is  sensitive  for  about  one  twen- 
tieth of  an  inch.     If  a  piece  of  caustic  is  applied  to  the  tip  (not 
more  than  1.5  mm.  from  the  very  end),  the  caulicle  will  curve 
awa3*  from  the  irritated  side.     The  reaction  is  as  plainly  seen  in 
those  cases  where  the  caulicle  does  not  elongate,  but  where  the 
root  itself  descends. 

1075.  The  length  of  the  portion  of  these  organs  which  reacts  is 
about  ten  millimetres.     The  time  of  reaction  varies  for  different 
plants,  being  sometimes  in  five  hours,  and,  according  to  Darwin, 
almost  always  within  twentj'-four  hours. 

1076.  "  The  curvature  often  amounts  to  a  rectangle  ;  that  is, 
the  terminal  part  bends  upwards  until  the  tip,  which  is  but  little 
curved,  projects  almost  horizontally.    Occasionally  the  tip,  from 
the  continued  irritation  of  the  attached  object,  continues  to  bend 
up  until  it  forms  a  hook  with  the  point  directed  towards  the 
zenith,  or  a  loop,  or  even  a  spire.     After  a  time   the  radicle 
apparently  becomes  accustomed  to  the  irritation,  as  occurs  in 
the  case  of  tendrils ;  for  it  again  grows  downwards,  although 
the  bit  of  card  or  other  object  may  remain  attached   to   the 
tip."  1 

1077.  The  tip  of  the  radicle  has  been  shown   (1046)  to  be 
constantly  circumnutating.     By  this  movement  the  sensitive  tip 
is  brought  into  contact  with  different  sides  of  minute  crevices  in 

1  Power  of  Movement  in  Plants,  1880,  p.  193. 


416  MOVEMENTS. 

the  soil,1  and  "  as  it  is  always  endeavoring  to  bend  to  all  sides, 
it  will  press  on  all  sides,  and  will  thus  be  able  to  discriminate 
between  the  harder  and  softer  adjoining  surfaces  .  .  .  conse- 
quently it  will  tend  to  bend  from  the  harder  soil,  and  will  thus 
follow  the  lines  of  least  resistance." 2 


1  Darwin  :  Power  of  Movement  in  Plants,  p.  197. 

2  The  two  following  passages  should  be  carefully  studied  by  the  student, 
since  they  embody  in  a  few  words  Darwin's  summary  of  most  of  the  results  ot 
his  experiments  upon  radicles.     Both  passages  are  from  the  "  Power  of  Move- 
ment in  Plants,"  1880  :  — 

"  We  see  that  the  course  followed  by  a  root  through  the  soil  is  governed  by 
extraordinarily  complex  and  diversified  agencies,  —  by  geotropism  acting  in  a 
different  manner  on  the  primary,  secondary,  and  tertiary  radicles,  —  by  sensi- 
tiveness to  contact,  different  in  kind  in  the  apex  and  in  the  part  immediately 
above  the  apex,  and  apparently  by  sensitiveness  to  the  varying  dampness  of 
different  parts  of  the  soil.  These  several  stimuli  to  movement  HIV  all  more 
powerful  than  geotropism,  when  this  acts  obliquely  on  a  radicle  which  has  been 
deflected  from  its  perpendicular  downward  course.  The  roots,  moreover,  of 
most  plants  are  excited  by  light  to  bend  either  to  or  from  it ;  but  as  roots  are 
not  naturally  exposed  to  the  light,  it  is  doubtful  whether  this  sensitiveness, 
which  is  perhaps  only  the  indirect  result  of  the  radicles  being  highly  sensitive 
to  other  stimuli,  is  of  any  service  to  the  plant.  The  direction  which  the  apex 
takes  at  each  successive  period  of  the  growth  of  a  root  ultimately  determines 
its  whole  course  ;  it  is  therefore  highly  important  that  the  apex  should  pursue 
from  the  first  the  most  advantageous  direction  ;  and  we  can  thus  understand 
why  sensitiveness  to  geotropism,  to  contact,  and  to  moisture,  all  reside  in  the 
tip,  and  why  the  tip  determines  the  upper  growing  part  to  bend  either  from  or 
to  the  exciting  cause.  A  radicle  may  be  compared  with  a  burrowing  animal 
such  as  a  mole,  which  wishes  to  penetrate  perpendicularly  down  into  the 
ground.  By  continually  moving  his  head  from  side  to  side,  or  circumnutating, 
he  will  feel  any  stone  or  other  obstacle,  as  well  as  any  difference  in  the  hard- 
ness of  the  soil,  and  he  will  turn  from  that  side  ;  if  the  earth  is  damper  on  one 
than  on  the  other  side,  he  will  turn  thitherward  as  a  better  hunting-ground. 
Nevertheless,  after  each  interruption,  guided  by  the  sense  of  gravity,  he  will 
be  able  to  recover  his  downward  course  and  to  burrow  to  a  greater  depth  " 
(p.  199). 

"We  believe  that  there  is  no  structure  in  plants  more  wonderful,  as  far  as 
its  functions  are  concerned,  than  the  tip  of  the  radicle.  If  the  tip  be  lightly 
pressed  or  burnt  or  cut,  it  transmits  an  influence  to  the  upper  adjoining  part, 
causing  it  to  bend  away  from  the  affected  side  ;  and,  what  is  more  surprising, 
the  tip  can  distinguish  between  a  slightly  harder  and  softer  object,  by  which 
it  is  simultaneously  pressed  on  opposite  sides. 

"  If,  however,  the  radicle  is  pressed  by  a  similar  object  a  little  above  the 
tip,  the  pressed  part  does  not  transmit  any  influence  to  the  more  distant  parts, 
but  bends  abruptly  towards  the  object.  If  the  tip  perceives  the  air  to  be 
moister  on  one  side  than  on  the  other,  it  likewise  transmits  an  influence  to  the 
upper  adjoining  part,  which  bends  towards  the  source  of  moisture.  When  the 
tip  is  excited  by  light  (though  in  the  case  of  radicles  this  was  ascertained  in 
only  a  single  instance)  the  adjoining  part  bends  from  the  light ;  but  when 


CIRCTJMNUTATION   OF   TENDRILS.  417 

1078.  Sensitiveness  of  stems  and  branches.     Under  ordinary 
conditions  even  twining  stems  are  not  sensitive  to  slight  mechani- 
cal irritation.     The  reactions  to  moisture,  light,  gravitation,  etc., 
have  been  already  noticed,  and  it  is  now  intended  to  call  atten- 
tion to  the  extraordinary  sensitiveness  of  certain  tendrils,  some 
of  which  are  modified  branches,  while  others  are  modified  leaves 
or  parts  of  leaves. 

1079.  Tendrils  circumnutate,  and  by  their  revolving  movement 
reach  out  for  a  proper  support.     Moreover,  they  are  produced 

on  the  young 
and  circum- 
nutating  ex- 
tremities of 

shoots,  so  that  two  modes  of  revolution 
are  frequently  to  be  observed  simulta- 
neously. But  in  this  revolving  move- 
ment the  tendrils  are  prevented  from 
becoming  entangled  with  the  rest  of  the 
shoot.  The  manner  in  which  this  is 
done  is  thus  described  :  ' '  When  a  ten- 
dril, sweeping  horizontally,  comes  round 
so  that  its  base  nears  the  parent  stem 
rising  above  it,  it  stops  short,  rises  stif- 
fly upright,  moves  on  in  this  position 
until  it  passes  by  the  stem,  then  rapidly 
comes  down  again  to  the  horizontal  po- 
sition, and  moves  on  so  until  it  again 
approaches  and  again  avoids  the  im- 
pending obstacle."  * 

1080.   When  a  light  thread  is  placed 
upon  a  long  revolving  tendril  of  Passiflora,   Echinocystis,   or 

excited  by  gravitation  the  same  part  bends  towards  the  centre  of  gravity.  In 
almost  every  case  we  can  clearly  perceive  the  final  purpose  or  advantage  of  the 
several  movements.  Two,  or  perhaps  more,  of  the  exciting  causes  often  act 
simultaneously  on  the  tip,  and  one  conquers  the  other,  no  doubt  in  accordance 
with  its  importance  for  the  life  of  the  plant.  The  course  pursued  by  the  radi- 
cle in  penetrating  the  ground  must  be  determined  by  the  tip  ;  hence  it  has 
acquired  such  diverse  kinds  of  sensitiveness.  It  is  hardly  an  exaggeration  to 
say  that  the  tip  of  the  radicle  thus  endowed,  and  having  the  power  of  directing 
the  movements  of  the  adjoining  parts,  acts  like  the  brain  of  one  of  the  lower 
animals  ;  the  brain  being  seated  within  the  anterior  end  of  the  body,  receiving 
impressions  from  the  sense  organs,  and  directing  the  several  movements" 

(p.  572). 

i  Gray  :  How  Plants  Behave,  1872,  p.  18. 

FIG.  187.    Shoot  of  Passiflora,  showing  tendrils. 

27 


418 


MOVEMENTS. 


Sicyos,  a  curvature  soon  takes  place  in  the  direction  of  the  con- 
tact. If  the  plant  is  in  a  vigorous  condition  and  the  tendril  is 
3"oung,  a  slight  touch  is  generally  sufficient  to  cause  immediate 
flexion.  If  a  solid  object,  for  instance  a  staff,  is  placed  in  con- 
tact with  such  a  tendril,  the  bending  and  coiling  takes  place  at 
once,  and  thus  the  organ  is  brought  into  close  apposition  with 
the  support. 

1081.  As  soon  as  the  tendril  has  coiled  around  its  support,  a 
striking  phenomenon  is  observed  in  the  portion  between  the  shoot 
and  the  support :  it  begins  to  twist,  throwing  the  whole  thread 
into  a  double  coil,  a  part  of  which  winds  one  way  and  the 
rest  another.  There  can  be  no  doubt  that  this  comes  from  the 
action  of  the  same  force  which  causes  the  revolution  in  the  ten- 
dril before  it  becomes  attached  to  the  support,  and  the  further 
exercise  of  this  force  must  necessarily  produce  two  coils  running 


in  opposite  directions.  After  the  tendril  has  made  fast  to  its 
support,  its  structure  begins  to  change  in  a  remarkable  manner, 
becoming  much  firmer  and  more  elastic  than  before,  — a  provision 
adapting  it  admirably  to  resist  sudden  strains  upon  the  main 
shoot  from  gusts  of  wind. 

1082.  But  if  the  tendril  in  its  revolution  has  failed  to  come  in 
contact  with  any  proper  support,  it  is  thrown  into  a  single  coil, 
which  runs  from  the  extremity  of  the  tendril,  and  extends  for 
a  short  distance,  perhaps  half  the  whole  length  of  the  organ. 
Sometimes,  however,  it  simply  becomes  flaccid. 


FIG.  188.    Ampelopsis  quinquefolia,  or  Virginia  creeper. 


SENSITIVENESS   O7/   LEAVES.  419 

1083.  In  some  cases  tendrils  are  not  sensitive  to  contact,  but 
are  distinctly  apheliotropic,  turning-  away  from  the  light,  and  in 
this  way  securing  for  the  plant  an  adequate  mechanical  support 
upon  some  wall  or  the  like.     Grape-vines  and  Virginia  creeper 
furnish  good  examples  of  such  tendrils.     The  branches  of  the 
tendrils  of  the  grape-vine  sometimes  clasp  around  a  slender  sup- 
port, somewhat  in  the  same  way  as  an  object  would  be  grasped 
by  a  thumb  and  finger. 

The  much-branched  tendrils  of  species  of  Ampelopsis  are  also 
apheliotropic  ;  but  when  the  tips  of  the  branches  of  the  tendrils 
come  in  contact  with  a  wall,  they  become  expanded  into  flat 
discs  which  cling  to  the  surface. 

1084.  Sensitiveness  of  petioles. 
This  can  be  easily  examined  in 
the  common  climbing  species  of 
Clematis,  in  Solanurn  jasm\noides, 
etc.      The  leaves   circumnutate 
and,   in  the  case   of  compound 
leaves,  the  separate  leaflets  also. 
When   }roung   the   sides   of  the 
petioles  are  sensitive  to  touch, 
bending  towards  where  the  pres- 
sure or  compact  is.    Shortly  after 
clasping  the  support  by  means  of 
this  bending  the  petioles  increase 
in    thickness,   become    stronger 
and    tougher  than   before,    and 
sometimes   take   on  a  structure 
suggestive  of  a  rigid  branch.    In 
Gloriosa  the  sensitiveness  is  very 
marked  in  the  leaf-tips,  but  only 
on  the  under  surface  of  the  pro- 
longed thread-like  extremity. 

1085.  Sensitiveness  of  leaf-blades.     The  fly-trap  of  Dionsea 
(considered  by  some  an  appendage  to  the  proper  leaf-blade)  is 
exquisitely  sensitive  to  any  touch  upon  the  hairs  which  grow  on 
the  faces  of  the  trap.     As  soon  as  these  are  touched  the  trap 
instantly  closes,  and  the  same  effect  follows  a  slight  touch  on 
the  median  line.     A  cross-section  through  the  leaf  shows  that 
the  parenchyma  is  thin- walled.     The  leaf  of  the  small  water- 
plant  Aldrovanda  has  likewise  been  shown  to  be  sensitive. 

FIG.  189.    Solanumjasiuinoides. 


420 


MOVEMENTS. 


1086.  The  leaflets  of  numerous  plants  exhibit  a  peculiar  degree 
of  sensitiveness  even  to  a  slight  touch.  Among  these  are  sev- 
eral species  of  Mimosa  and  Oxalis. 
The  plant  which  has  received  the 
fullest  investigation  is  the  easily 
cultivated 

1087.  Mimosa  pudica  (the  Sen- 
sitive plant).  This  has  compound 
leaves  consisting  of  four  long  leaf- 
lets, each  of  which  is  divided  into 
numerous  minor  leaflets  arranged 
in  pairs.  At  the  base  of  each  leaf- 
let, and  also  at  the  base  of  the 
petiole,  there  is  a  pulvinus,  com- 
posed of  peculiar  cells.  On  the 
upper  half  of  the  pulvinus  these 
are  thicker-walled  than  on  the 
lower ;  most  of  them  contain  round- 
ish globules  made  up  of  a  strong 
solution  of  tannin  in  water,  surrounded  by  a  film  of  some  albu- 
minoid matter.  These  globules  are  not, 
however,  of  any  significance  as  concerns  the 
motility,  since  they  are  found  in  the  paren- 
chyma of  the  bark  of  some  ligneous  plants 
(see  953). 

1088.   When  a  fully  spread  leaf  is  touched 
at  its  extremity  the  many  leaflets  succes- 
sively  close    in   pairs,    the    upper   surfaces 
approaching  and  the  tips  falling  somewhat 
forward;    the  four 
branches  of  the  leaf 
then  draw  near  each 
other,  and  the  main 
petiole   inclines 
downwards  and 
finally  droops  pas- 
sively at  the  joint. 
The  recovery  from 
this  position  of  col- 
lapse takes  place  in 
a  few  minutes,  generally  in  about  a  quarter  of  an  hour. 

Fm.  190.    Al.lrovanda  vesiculosa;  the  lower  illustration  shows  the  expanded  leaf 
much  enlarged. 

FIG.  191.    Mimosa  pudica. 


SENSITIVE   PLANT.  421 

1089.  If  an  irritant  is  applied  to  a  single  leaflet,  the  opposite 
one  may  be  the  only  other  affected ;  or,  if  the  effect  is  more  pro- 
nounced, all  the  leaflets  on  a  single  division  of  the  leaf  may  be 
closed  without  affecting  any  on  the  other  branches.    But  if  a  still 
sharper  impulse  is  given,  not  only  will  all  the  leaflets  on  a  single 
leaf  close,  but  other  leaves  on  the  plant  may  be  affected.     Thus 
it  is  possible  by  applying  a  hot  needle  to  a  single  leaflet  to  affect 
all  those  on  a  small  plant.     A  drop  of  strong  sulphuric  acid  acts 
in  the  same  way.1 

When  a  leaf  of  Mimosa  is  separated  from  its  plant  by  a  sharp 
cut  through  its  pulvinus,  and  is  at  once  placed  in  a  saturated 
atmosphere,  it  soon  recovers  its  normal  expanded  condition ;  if 
now  it  is  touched  the  leaflets  will  collapse  as  usual,  and  at  the 
moment  of  closing  a  drop  of  water  can  be  seen  exuding  from  the 
cut  surface.  According  to  Pfeffer  it  is  possible  to  observe  that 
the  water  comes  from  the  parenchyma  of  the  lower  half  of  the 
pulvinus.2 

1090.  According  to  Bert,8  who  made  use  of  a  thermo-electric 
apparatus,  the  pulvinus  of  a  leaf  of  Mimosa  in  its  normal  condi- 


1  For  a  study  of  the  transmission  of  the  shock,  see  Pfeffer,  Pringsheim's 
Jahrbiicher,  ix.,  1873,  p.  308. 

Some  of  the  effects  produced  by  irritants  upon  the  hairs  of  certain  insectiv- 
orous plants  have  been  already  described.  The  phenomena  of  aggregation 
then  alluded  to  must  be  now  treated  more  in  detail.  It  is  described  by  Pfeffer 
in  the  following  words :  "  Suddenly  the  contents  of  the  cell  acted  on  become 
clouded  by  a  separation  of  minute  particles  which  aggregate  to  form  masses. 
These  masses  consist  essentially  of  albuminous  matters,  which,  from  their  col- 
lecting the  coloring  substance  in  the  cell-sap,  become  tinged.  The  whole 
process  of  aggregation  takes  place  in  the  cell-sap." 

Pfeffer  points  out  the  curious  fact  that  while  ammonic  carbonate,  without 
any  other  irritant,  will  cause  this  aggregation,  acetic  acid  will  make  it 
disappear. 

Such  changes  as  aggregation  and  variations  in  turgescence  are  connected  in 
some  way,  not  yet  understood,  with  the  imbibition  power  of  protoplasm  for 
watery  fluids.  The  mechanical  or  chemical  irritants  which  temporarily  dimin- 
ish the  capacity  of  protoplasm  for  retaining  within  the  cell  the  maximum 
quantity  of  water  will  produce  a  distinct  effect  upon  the  tension  of  the  cell- 
wall,  and  result  in  a  change  of  its  size  or  form,  or  both.  The  irritation  thus 
caused  can  be  transmitted  to  a  distant  part.  The  intimate  relations  which 
exist  between  the  young  cell-wall  and  the  protoplasmic,  lining  must  not  be 
overlooked  in  any  consideration  of  the  subject  of  sensitiveness  in  plants. 
Lastly,  the  continuity  of  protoplasm  in  many  mobile  and  sensitive  organs  must 
be  borne  in  mind  in  the  consideration  of  this  subject. 

2  Pflanzenphysiologie,  ii.,   1881,  p.  237.     See  also  Pfeffer's  Physiologische 
Untersuchungen,  1873,  p.  32. 

8  Comptes  Eendus,  Ixix.,  1869,  p.  895. 


422 


MOVEMENTS. 


tion  is  always  slightly  cooler  than  the  rest  of  the  petiole,  but 

upon  the  movement  from  irritation  it  rises  in  temperature  ;  not 

enough,  however, 
to  account  for  the 
raising  of  so  con- 
siderable a  weight 
as  that  of  the  leaf. 
1091.  Some 
physiologists  have 
regarded  the  sen- 
sitiveness of  the 
pulvinus  of  the 
Sensitive  plant 
and  of  other  motile 
parts  as  residing 
chiefly  if  not  whol- 
ly in  the  cell- wall, 
while  others  have 

thought  that  it  resided  in  the  contractile  protoplasm.     It  is  now 

generally  held  to  be  due  to  some  sudden  variation  in  the  osmotic 

power    of  the    proto- 
plasm, particularly  in 

its  peripheral  portion 

in    contact    with    the 

cell- wall,  by  which  the 

turgescence  of  the  cell 

is  suddenly  changed.1 
1092.    If    a    plant 

with  motile   leaves  is 

kept  in   darkness   for 

a  da}r  or  so,  even  if 

the  temperature  is  fav- 
orable to   motion,  its 

power  of  movement  is 

either  greatly  impaired 

or  for  a  time  wholly  193 

lost.      A    diminished 

amount  of  light  is  sufficient  to  produce  the  same  effect  in  the 

case  of  the  Sensitive  plant. 

1  Compare  Hofmeister :  Die  Lehre  von  der  Pflanzenzelle,   1867,   p.   300  ; 

Briicke  :  Archiv  fiir  Anatomic,  Physiologic,  und  wiss.  Medicin,  1848,  p.  434  ; 

linger  :  Botanische  Zeitung,  1862,  p.  113  ;  1863,  p.  349. 

FIG.  192     Transverse  section  of  the  motile  organ  of  a  leaflet  of  Oxalis  carnea.  (Sachs.) 
FIG.  193.    Vertical  section  through  tlie  motile  organ  of  a  leaflet  of  Oxalis  carnea. 

(Sachs.) 


SENSITIVENESS    OF    STAMENS.  423 

Sachs  has  given  the  name  Phototonus  to  the  normal  motile 
condition  resulting  from  alternation  of  day  and  night.  ' "  A 
plant  in  this  condition,  if  placed  in  the  dark,  will  remain  for  some 
time  (hours  or  even  days)  in  a  state  of  phototonus,  which  then 
disappears  gradually  ;  the  plant  is  therefore  under  normal  condi- 
tions in  a  state  of  phototonus  even  during  the  night.  In  the 
same  manner  a  plant  which  has  become  rigid  in  continued  dark- 
ness retains  its  rigidity  for  some  time  (hours  or  even  days) 
after  being  exposed  to  light.  The  two  conditions  therefore 
pass  over  into  one  another  only  slowly." 

1093.  Temporary  rigidity  is  produced  in  the  case  of  the  Sensi- 
tive plant  by  an  exposure  to  a  temperature  of  15°  C.    The  same 
effect  is  produced  by  a  temperature  above  50°  C.,  according  to 
Bert's  observations  at  about  60°  C.    It  is  stated  by  him  that  the 
sensitiveness  of  Mimosa   is  destro3red  by  exposure  to  a  green 
light,  while  plants  placed  under  bell-jars  of  the  following  colors 
remained  healthy  :  white,  red,  yellow,  blue,  and  violet.1 

1094.  Sensitiveness   of  stamens.      No   better   illustration   of 
this  is  afforded  than  that  given  by  stamens  of  the  common  Bar- 
berry.   The  six  stamens  lie  curved  under  the  arching  petals,  but 
if  a  filament  is  lightly  touched  it  is  jerked  suddenly  forward, 
bringing  the  anther  into  apposition  with  the  pistil. 

1095.  The  filaments  of  certain  Composite  are  sensitive.    The 
case  of  the  common   Chicory  has   been   thus   described :   The 
anthers  are  conjoined  to  form  a  tube  supported  upon  five  dis- 
connected filaments  which  are  at  first  more  or  less  curved  out- 
wards.    If  the  filaments  in  this  condition   are  lightly  touched 
they  instantly  straighten,   carrying  the  anther-tube  up  a  little 
higher,  and  thus  bringing  the  pollen  all  along  the  style  which  is 
enclosed.     After  a  short  time  they  resume  their  former  curved 
condition,  retracting  the  anther-tube  to  the  place  which  it  occu- 
pied before.     It  is  to  be  observed  that  the  irritation  of  a  single 
filament  excites  only  that  one,  and  thus  the  tube  of  anthers  may 
be  pushed  over  to  one  side  for  a  few  minutes,  again  recovering 
itself  after  a  little  while. 

1096.  Sparmannia  Africana  has  a  cluster  of  beaded  filaments 
surrounding  the  pistil  and  variously  intermingled  with  the  sta- 
mens.    When  these  are  touched  lightty  they  open  out  from  the 
centre  with   considerable   rapidity,  and  remain  thus  expanded 
for  a  certain  period,  after  which  they  revert  to  the  closed  posi- 
tion.    Somewhat  the  same  phenomenon  is   to  be  observed  in 

1  Comptes  Rendus,  Ixx.,  1870,  p.  339. 


424  MOVEMENTS. 

species  of  Portulaca,  where  the  stamens,  upon  contact,  move 
outwards. 

1097.  The  gynandrous  style  of  Stylidium  is  curved  down- 
wards ;  when  it  is  lightly  touched  it  suddenly  flies  to  the  other 
side  of  the  flower,  although  sometimes  it  merely  straightens 
itself. 

Sensitive  lobes  of  the  style  or  stigma  are  possessed  by  Mimu- 
lus  and  some  other  Scrophulariaceae,1  by  Martynia,  and  some 
allied  plants. 

1098.  In  all  the  foregoing  cases  the  sensitiveness  is  greatest 
when  the  plants,  or  their  sensitive  parts,  are  kept  at  a  tolerably 
high  temperature.     Sachs  has  shown  that  the  most   favorable 
temperature  for  Mimosa  movements  is  about  36°  or  37°  C. 

1099.  Effects  of  anaesthetics  upon  sensitiveness  in  plants.    When 
a  young  plant  of  Mimosa  is  placed  under  a  bell-jar  in  which  a 
sponge  wet  with  chloroform  or  an   equivalent   anaesthetic  has 
filled  the  confined  atmosphere  with  its  vapor,  some  of  the  leaflets 
droop  and  remain  so,  while  others  retain  their  normal  position. 
But  after  a  while  the  leaflets  will  be  found  to  have  lost  all  power 
of  reacting  to  a  touch ;  in  short,  they  have  become  insensitive. 
The  same  effect  is  observed  in  the  case  of  Barberry  stamens. 
Its  explanation  is  looked  for  in  the  changed  relation  of  the 
sensitive  cells  to  water  when  they  are  subjected  to  the  influence 
of  an  anaesthetic. 

1100.  Plants  possess  no  nervous  system.    That  sensitive  plants 
must  have  nerves,  or  tbeir  equivalent,  for  the  recognition  of  im- 
pressions and  the  transirission  of  their  influence  to  a  somewhat 
distant   point  was   formerly  held   by   many   writers,    but    this 
opinion  is  not  now  entertained  by  any  physiologist.2 

»  See  Heckel's  Memoir,  Coraptes  Rendus,  Ixxix.,  1874,  p.  702. 

3  "  Finally,  it  is  impossible  not  to  be  struck  with  the  resemblance  between 
the  foregoing  movements  of  plants  and  many  of  the  actions  performed  uncon- 
sciously by  the  lower  animals.  With  plants  an  astonishingly  small  stimulus 
suffices  ;  and  even  with  allied  plants  one  may  be  highly  sensitive  to  the  slight- 
est continued  pressure,  and  another  highly  sensitive  to  a  slight  momentary 
touch.  The  habit  of  moving  at  certain  periods  is  inherited  both  by  plants  and 
animals  ;  and  several  other  points  of  similitude  have  been  specified.  But  the 
most  striking  resemblance  is  the  localization  of  their  sensitiveness,  and  the 
transmission  of  an  influence  from  the  excited  part  to  another,  which  conse- 
quently moves.  Yet  plants  do  not  of  course  possess  nerves  or  a  central  ner- 
vous system  ;  and  we  may  infer  that  with  animals  such  structures  serve  only 
for  the  more  perfect  transmission  of  impressions,  and  for  the  more  complete 
intercommunication  of  the  several  parts  "  (Darwin  :  Power  of  Movement  in 
Plants,  1880,  p.  571). 


CHAPTER  XIV. 

REPRODUCTION. 

1101.  IN  scientific  as  well  as  popular  language  the  term  indi- 
vidual is  commonly  applied  to  each  and  every  plant ;  but  if  by 
individual  is  meant  an  organism  incapable  of  subdivision  with- 
out loss  of  its  identity,  the  term  as  applied  thus  to  the  higher 
plants  is  obviously  a  misnomer.    It  has  been  shown  both  in  Vol- 
ume I.  of  this  series,1  and  in  Part  I.  of  the  present  volume,2  that 
under  certain  circumstances  any  of  the  higher  plants  may  be 
separated  into  parts,  each  of  which  may  afterwards  lead  an  inde- 
pendent existence.     Thus  buds  may  be  severed  from  the  parent 
plant  and  soon  establish  themselves  as  independent  organisms, 
capable  of  increase  in  size,  and  becoming  sooner  or  later  dis- 
tinguishable in  no  wise  from  the  stock  from  which  they  came. 
But  there  are  serious  difficulties  in  the  way  of  regarding  these 
separable  buds  as  true  individuals : 8  each  bud  is  the  promise  of 
a  branch,  and  consists  of  parts  which,  under  certain  conditions, 
may  be  separated  from  each  other.     In  fact,  the  vegetable  indi- 
vidual is  not  reached  in  such  mechanical  subdivision  until  we 
come  to  the  cells  of  which  all  the  parts  are  composed.     Nor  do 
these  satisfy  completely  the  definition  of  an  individual,  since  in 
exceptional  cases  the  cell  itself  may  spontaneously  divide  into 
viable  parts.4 

1102.  In  plants,  individuality  is  more  or  less  completely  merged 
in  community.      Under  normal  conditions   the  separable  parts, 
while  still  attached  to  their  common  stock,  co-operate  for  the 
common  good.      If  separated  under  favorable  conditions  they 
in  their  turn  become  stocks  in  which  are  combined  congeries  of 
similar  separable  parts,  or,  in  other  words,  become  individual 
plants,  in  the  ordinary  acceptation  of  the  term.     For  instance, 
the  tuber  of  the  potato,  which  is  the  thickened  extremitj-  of  an 
underground  branch,  possesses  a  certain  number  of  buds,  each 

1  Page  31 G.  2  Pages  152,  162.  8  Volume  i.  p.  316. 

4  Such  a  phenomenon  is  seen  in  the  formation  of  swarm-spores  (or  zobgo- 
nidia)  from  a  terminal  cell  of  Achlya. 


426  REPRODUCTION. 

of  which  may,  in  suitable  soil,  give  rise  to  a  thrifty  plant :  the 
new  plants  will  in  their  turn  produce  new  tubers  likewise  with 
buds,  and  these  again  new  plants,  and  so  on  in  unlimited 
succession.  Nevertheless,  the  divisible  organisms  are  for  our 
present  purpose  conveniently  termed  vegetable  individuals.1 

1103.  Plants  of  the  higher  grade  (Phaenogamous  plants)  are 
propagated  either  by  buds  or  by  seeds.     In  the  former  case,  a 
portion  of  the  axis  with  incipient  leaves  is  separated  from  the 
parent ;  in  the  latter  case,  a  new  structure  (the  embryo) ,  capa- 
ble of  independent  existence,  is  formed  by  means  of  a  special 
apparatus,  —  the  flower.     In  the  flower,  two  sets  of  sexual  or- 
gans, the  stamens,  constituting  the  androecium,  and  the  pistils, 
constituting  the  gyucecium,  produce  by  their  conjoint  action  an 
embryo,  or  undeveloped  plant,  within  the  seed. 

Reproduction  by  buds  is  non-sexual  or  asexual ;  that  by  the 
formation  of  an  embryo  is  sexual. 

1104.  Non-sexual  reproduction  (Agamogenesis)  can  be  traced 
through  all  classes  of  plants,  —  from  the  higher,  where  it  takes 
place  through  proper  buds,  down  to  the  very  lowest,  where  it 
takes  place  by  a  single  cell  dividing  spontaneously  to  form  two 
or  more  separated  individuals. 

1105.  Sexual   reproduction  (Gamogenesis)  likewise  can  be 
traced   through   all   classes  of  plants  except  the  very  lowest, 
where   it  has  not  as  yet  been  demonstrated  to  exist.     As  the 
series  is  followed  from  above  downwards,  the  flower  gives  place 
to  other  structures,  and  the  seed  is  replaced  by  simpler  bodies, 
known  as  spores. 

FERTILIZATION  IN  ANGIOSPERMS. 

1106.  Flowering  plants  are  naturally  divided  into  Angio- 
sperms  and  Gymnosperms :  the  former  are  distinguished  by  the 
possession  of  a  closed  ovary  in  which  the  ovules  are  contained. 
The  latter  have  no  closed  ovary,  and  hence  the  ovules  are  naked. 
A  part  of  the  reproductive  apparatus  is  simpler  in  Gymnosperms 
than  in  Angiosperms ;  but  owing  to  certain  practical  difficulties 
in  the  treatment  of  microscopic  material,  the  demonstration  of 
the  reproductive  process  is  less  easy  in  the  former  than  in  the 
latter.     It  is  proposed,  therefore,  to  begin  with  an  examination 
of  the  reproductive  process,  or  fertilization,  of  Angiosperms. 

1  The  view  has  been  held  by  some  that  all  the  derivatives  from  one  seed, 
whether  united  or  separated,  constitute  collectively  a  single  individual. 


STUUUTUUE    OF    THE    PISTIL.  427 

1107.  Three  subjects  must  be  briefly  reviewed  before  enter- 
ing upon  the  study  of  the  process  itself;  namely,  the  pistil,  the 
ovule,  and  the  pollen-grain.     For  all  details  regarding  particu- 
lars of  form  and  special  morphological  relations,  pages  249-285 
of  Volume  I.,  and  Chapter  IV.  of  the  present  volume  ma}-  be 
consulted. 

1108.  The   angiospermous   pistil  (see  Fig.  196)  consists  of  a 
closed  ovary  containing  the  ovules,  which  is  generally  prolonged 
into  a  slender  organ  known  as  the  style.     Either  some  portion  of 
the  style,  or,  when  this  is  wanting,  some  portion  of  the  ovary,  is 
furnished  with  a  peculiar  secreting  surface  known  as  the  stigma. 
The  manifold  shapes  of  ovary,  style,  and  stigma  have  been  suf- 
ficiently described  in  Volume  I.,  and  the  microscopic  structure 
of  each  has  been  examined  in  a  general  way  in  Part  I.  of  the 
present  volume.     From  what  was  there  said,  it  will  be  remem- 
bered that  the  form  and  structure  of  pistil  and  stamens  have 
intimate  relations  to  the  transfer  of  pollen  and  its  reception  by 
the  stigma. 

1109.  The  stigmatic  secretion.     The  surface  from  which  this 
exudes  may  exist  as  an  expanse  of  considerable  extent,  or  it 
ma}'  have  the   form  of  single   or  double   lines,  or  be  reduced 
even  to  a  mere   point.      The  extent  of  the  stigmatic   surface 
bears  a  fixed  relation  to  the  number  of  ovules  in  the  ovary. 

At  a  certain  period  in  the  development  of  the  flower,  the 
stigma,  which  up  to  that  time  may  have  been  apparently  free 
from  moisture,  becomes  covered  with  a  glutinous  secretion  of 
a  saccharine  nature.  At  this  period,  known  as  that  of  ma- 
turity, the  stigma  is  from  its  stickiness  likely  to  catch  and 
retain  upon  its  surface  any  pollen  which  may  fall  thereon. 
The  secretion  is  generally  slightly  acid  x  in  reaction,  and  is  as 
variable  in  the  amount  of  sugar  which  it  contains  as  ordinary 
nectar. 

1110.  The  pollen-grains  of  angiosperms  when  set  free  from 
the  cells  in  which  they  are  produced  may  become  completely 
isolated  (simple  grains),  or  they  may  remain  firmly  coherent  in 
clusters  of  four  (Typha,  Rhododendron,   etc.),  eight,  sixteen, 
thirty-two,  or   even,  as  in  some  species  of  Acacia,  sixty-four 
("compound   grains").     In  many  Orchidacese  the  grains  are 
more  or  less  compact!}7  fastened  together  into  masses  by  a  glu- 
tinous matter  forming  poUinia,  and   much  the  same  grouping 
into  masses  occurs  in  Asclepiadaceae. 

1  Van  Tieghem  :  Traite  de  Botanique,  1884,  p.  850. 


428  KEPRODUCTION. 

1111.  Structure  of  pollen-grains.1     The  grains  consist  of  sin- 
gle cells  having  a  firm  membrane  and  heterogeneous  contents. 
The  membrane  is  rarely  single  (as  in  Zostera),  being  generally 
composed  of  two  coats,  —  an  outer,  the  extine  (called  exine  by 
Schacht),  and  an  inner,  the  inline.     The  extine  may  be  smooth, 
but  it  is  frequently  beset  with  protuberances  of  some  kind,  points, 
prickles,  or  other  sculpturings,  which  may  be  characteristic  of 
genera  or  even  larger  groups.      It  is  also  provided  generally 
with  one  or  more  partial  or  complete  perforations,  which  are  of 
course  fully  closed  by  the  intine  which  is  pressed  up  against 
them.     The  number  of  these  perforations  is  constant  in  certain 
groups  of  plants :  for  instance,  one  in  most  monocot3'ledonous 
plants  ;  two  in  Ficus,  Justicia,  Beloperone  ;  three  in  Onagracese, 
Geraniacese,  Composites ;  four  to  six  in  Jmpatiens,  Ulmus,  and 
Alnus ;  many  in  Nyctaginaceae,  Convolvulaceae,  Malvaceae,  and 
some  Caryophyllaceae.     Under  the  action  of  concentrated  sul- 
phuric acid  the  intine  is  destroyed,  while  the  extine  generally 
remains  unchanged  except  in  color.2 

When  the  pollen  of  Thunbergia  is  acted  on  by  strong  sulphuric 
acid,  the  destruction  of  the  intine  permits  the  extine  to  uncoil 
as  a  band.  In  no  case  did  Schacht  detect  any  perforation  of 
the  intine. 

1112.  The  contents  of  a  pollen-grain  are  (1)  protoplasmic  mat- 
ter; (2)  granular  food  materials,  such  as  starch,  oil,  and,  ac- 
cording to  Schacht,  inulin ;    (3)  dissolved  food  matters,  sugar 
and   dextrin.     These  heterogeneous   contents   form   what   was 
formerly  called  the  fovilla. 

In  the  granular  protoplasmic  matter  of  pollen-grains  it  is  pos- 
sible to  demonstrate  the  existence  of  a  nucleus,  and  in  some 
cases  two  nuclei  can  be  made  out  distinctly.  It  is  considered 
well  established8  that  the  single  nucleus  which  exists  in  the 
simple  grain  at  the  period  of  its  separation  from  the  mother-cell 
divides  in  most  cases  into  two  nuclei  of  unequal  size.  The  larger 
of  the  two  fragmental  nuclei  remains  with  no  change ;  while  the 
smaller  may  become  partitioned  off  from  the  rest  of  the  cell  either 
by  a  true  cell-wall  or  by  a  peripheral  film  of  protoplasm,  and  may 
later  divide  and  form  a  group  of  two  or  four  minute  cells. 

1  These  details  are  summarized  chiefly  from  Schacht's  exhaustive  treatise 
on  the  subject  in  Pringsheim's  .Tahrbiicher,  ii.,  1860,  p.  109. 

a  In  some  cases  a  double  membrane  can  be  shown  in  the  extine,  for  instance 
(Enothera,  where  the  extine  separates  into  a  true  extine  and  an  intextine. 

8  Strasburger :  Ueber  Befruchtung  und  Zelltheilung,  1878.  See  also 
Quarterly  Journal  of  Microscopical  Science,  1880,  p.  19, 


POLLEN-GRAINS. 


429 


1113.  The  pollen-grains  of  many  plants  burst  when  placed  in 
water,  and  the  fovilla  escapes  as  a  slightly  coherent  mass  which 
soon  becomes  more  diffused  and  allows  the  finer  granules  to  pass 
into  the  water,  where  they  immediately  exhibit  the  Brownian 
movement,   common   to  all    minute    particles   suspended   in   a 
liquid.1 

1114.  If  pollen-grains  are  placed  in  a  solution  of  sugar  in- 
stead of  in  pure  water,   they  will  increase  somewhat  in  size ; 
and  in  a  few  hours,  if  the  specimen  is  kept  at  the  right  tem- 
perature, there  will  appear  at  some  point  of  the  surface  of  each 


grain  a  minute  tube,  which  by  great  care  can  be  cultivated  in  a 
proper  medium  until  it  attains  a  length  of  several  millimeters.2 

1115.  The  pollen-grains  of  Tulipa  Gesneriana  emit  their  tubes 
in  a  1  to  3  per  cent  solution  of  cane-sugar ;  the  following  require 
a  somewhat  stronger  syrup :  Leucojum  sestivum  and  Narcissus 
poeticus,  3  to  5  per  cent ;  most  orchids,  5  to  10  per  cent;  Con- 
vallaria  majalis,  5  to  20  per  cent ;  Iris  sibirica,  30  to  40  per 
cent.8 


1  For  an  extended  account  of  the  speculations  once  based  upon  the  occur- 
rence in  water  of  motion  of  the  particles  of  the  fovilla,   the  reader  should 
consult  Meyen:  Pflanzenphysiologie,  iii.,  1839,  pp.  192  et  seq. ;  and  also  the 
remarkable  treatise  by  Robert   Brown. 

2  Schleiden  states  that  pollen-grains  which  come  accidentally  in  contact 
with  nectar  readily  send  out  tubes  ;  and  that  we  often  find  at  the  base  of  the 
flower  a  whole  mass  of  confervoid  web,  which  consists  of'entangled  pollen- 
tubes  emitted  in  this  manner  (Principles  of  Scientific  Botany,  1849,  p.  408). 

8  Strasburger :  Das  botanische  Practicum,  1884,  p.  511. 

FIG.  194.  a,  young  pollen-grain  of  Allium  fistulosum,  before  its  division  ;  b,  after  the 
division  of  the  nucleus :  c,  after  the  division  of  the  protoplasm ;  d,  young  pollen-grain  of 
Monotropa  Hypopitys  divided ;  e,  same  emitting  its  tube,  into  which  the  two  nuclei 
pass;  /.  coalescent  grains  of  the  pollen  of  Platanthera  bifolia  during  their  division  ;  g, 
formation  of  the  pollen-tube  of  Orchis  mascula,  into  which  the  two  nuclei  pass.  (Stras- 
burger J 


430  REPRODUCTION. 

1116.  When  a  pollen-grain  is  deposited  upon  a  fitting  stigma,1 
at  the  period  when  the  stigmatic  secretion  is  sufficiently  abun- 
dant, it  increases  somewhat  in  size,  and  soon2  a  tube,8  sometimes 
more  than  one,  is  thrust  forth  and  passes  immediately  into  the 
loose  tissue  of  the  stigmatic  surface.  The  tube  consists  of  a 
protrusion  of  the  intine,  and  its  place  of  emerging  is  at  some 
one  of  the  perforations  of  the  cxtine.  In  some  instances  the 
wall  separating  the  larger  and  the  smaller  fragments  of  the 
original  nucleus  of  the  pollen-grain  becomes  absorbed,  and 
then  the  two  nuclei  make  their  way  into  the  tube  as  it  is 


prolonged.  During  its  descent  the  pollen-tube  is  slender,  of 
about  the  same  calibre  throughout,  and  has  extremely  thin 
walls.  It  extends  through  the  conducting  tissue  of  the  style, 
being  nourished  by  the  nutrient  matter  secreted  from  the  cells  of 
that  tissue,  until  it  at  last  reaches  the  cavity  of  the  ovary. 

1117.  According  to  Capus,4  the  extent  of  the  stigmatic  surface 
bears  a  definite  relation  to  that  of  the  conductive  tissue  of  the 
style,  one  surface  being  in  fact  a  mere  expansion  of  the  other ; 
aiid  the  volume  of  the  conductive  tissue  of  the  style  is  governed 
by  the  number  of  ovules  which  are  to  be  fertilized.  Thus,  in  a 

1  An  interesting  account  of  the  artificial  fertilization  of  certain  plants  of 
the  Poppy  family  after  removal  of  the  stigmas  is  given  by  Hooker  in  "  The 
Gardeners'  Chronicle,"  1847.     It  is  not  known  that  the  experiments  have  yet 
been  repeated. 

2  According  to  Gartner,  the  emission  of  the  pollen-tube  begins  in  some 
cases  in  half  a  minute  after  the  pollen  has  been  applied  to  the  stigma  ;  but  in 
some  others,  as  in  Mirabilis  Jalapa  and  in  the  Malvaceae,  it  takes  from  24 
to  36  hours. 

8  Amici,  in  1822,  appears  to  have  been  the  first  to  detect  the  pollen-tube. 
His  earliest  observations  were  made  upon  Portulaca  oleracea. 
4  Annales  des  Sc.  nat.,  ser.  6,  tome  vii.  p.  204. 

FIG.  195.  Apparatus  for  cultivating  pollen-grains,  etc.  The  object  is  placed  on  tlf 
under  side  of  a  glass  cover  over  the  circle  at  a.  If  necessary,  air  can  be  drawn  through 
the  tube.  A  simpler  contrivance  may  bo  made  from  a  piece  of  moist  pasteboard. 


DESCENT   OF   THE  POLLEN-TUBE.  431 

pistil  with  a  large  number  of  ovules  the  stigmatic  surface  is 
large,  as  is  also  the  amount  of  conductive  tissue  of  the  style 
through  which  the  pollen-tubes  are  to  descend. 

1118.  The  conductive   tissue   through  which   the   pollen-tube 
descends,  and  by  which  it  is  nourished,  is  formed  at  the  stigma 
by  a  modification  of  epidermal  cells,  and  below  this  arises  from 
modifications  in  the  parenchyma  ;  in  the  style  it  may  constitute 
a  solid  mass  of  delicate  cells,  sometimes  with  walls  which  have 
undergone  the  mucilaginous  modification,  or  it  may  simply  line 
the  hollow  tube   which   is   frequently  found,  as  in  the  pistil  of 
the  violet. 

1119.  The  time  required  for  the  descent  of  the  pollen-tube  de- 
pends  upon  the  length  and  character  of  the  path  the  tube  is 
to  traverse,  and  is  very  different  in 

different  cases.  Hofmeister  states 
that  in  Crocus  vernus,  with  a  style 
which  is  from  one  to  two  inches  in 
length  or  sometimes  more,  the  tube 
reaches  the  ovary  in  from  one  to 
three  days.  Schleiden l  gives  the 
following  times  required  for  descent 
of  the  tube :  Cereus  grandiflorus, 
having  a  style  nine  inches  long,  a 
few  hours ;  Colchicum  autumnale, 
with  a  style  thirteen  inches  long, 
twelve  hours.  In  some  other  cases 
(certain  orchids)  it  is  weeks  before 
the  end  of  the  tube  has  descended 
for  even  a  veiy  short  distance. 

1120.  A   single   pollen-grain  of 
some  flowers  can  emit  more  than 
one   pollen-tube  :    thus   Amici   has 
seen  twenty  to  thirty  tubes  proceed 

from  one  grain.  Pollen-tubes  sometimes  branch  in  their  course 
downward. 

1121.  The   length   of    time   during  which  pollen-grains  can 
preserve  their  vitality  has  been  determined  for  a  few  cases : 2 

1  Schleiden:  Principles  of  Scientific  Botany,  1849,  p.  407. 

2  Gartner,  quoted  by  Mohl :  Vegetable  Cell,  p.  134. 

PtG  196.  Diagram  of  a  longitudinal  section  of  an  ovary  having  only  one  ovule  with 
basal  placentation,  designed  to  exhibit  the  course  of  the  pollen-tube  from  the  stigma  to 
the  summit  of  the  embryonal  sac  above  the  oosphere.  The  ovule  is  anatropous,  and 
is  inserted,  as  is  usually  the  case  in  Composite.  (Luerssen.) 


432  REPRODUCTION. 

Those  of  Hibiscus  Trionum  at  least  three  days  after  removal 
from  the  anther ;  those  of  Chcirauthus  Cheiri,  fourteen  days  ; 
those  of  Camellia,  Cannabis,  Zea,  and  Phrenix  dactylifera  (Date), 
one  year. 

1122.  Although  each  ovule  requires  for  its  impregnation  only 
one  pollen-tube,  the  number  of  pollen-grains  in  flowers  which 
open  at  maturity  is  far  in  excess  of  the  number  of  ovules.     The 
ratio  has  been  ascertained  in  a  few  cases,   among  which  are 
the  following :    Cereus  grandiflorus,1  250,000  grains  of  pollen 
to  30,000  ovules ;    Wistaria   sinensis,2   about  7,000   grains   of 
pollen  to  each  ovule ;  Hibiscus  Trionum,8  4,863  grains  of  pol- 
len to  about  30  ovules.    In  some  other  cases,  for  instance  Geum 
urbanum,4  the  excess  of  pollen  over  ovules  is  about  10  : 1. 

1123.  The  localization  of  the  conductive  tissue  in  the  ovary 
itself  is  sometimes  very  marked ;  thus  in  ovaries  with  parietal 
placentation,  the  ovarian  walls  in  the  immediate  vicinity  of  the 
ovules  are  seen  to  be  distinctly  conductive,  while  in  those  with 
axile   placentation,  the   modified  tissue   is  found  in  the   axis. 
Capus  distinguishes  the  following  varieties  of  conductive  pla- 
centae :  (1)  with  a  smooth  surface,  the  micropyle  being  close 
to  the  placenta,  e.  g.,  Solanum  ;  (2)  papillar,  the  papillae  either 
simple  or  compound,  sometimes  serving  to  guide  the  pollen-tube 
to  the  micropyle,  e.  g.,  some  Cucurbitaceae  ;   (3)  hairy,  the  hairs 
sometimes  secreting  a  mucus  or   even   breaking   down   into  a 
gelatinous  mass  through  which  the  pollen-tube  may  penetrate 
with  facility,  e.  g.,  some  Aroids.     Special  names  were  formerly 
given  to  peculiar  forms  of  the  conductive  tissue,  but  the  terms 
now  possess  no  utility.     For  special  examples  of  the  forms,  the 
reader  must  consult  the  practical  exercises  at  the  end  of  this 
volume. 

1124.  Structure  of  the  ovule.     As  shown  on  page  175,  the 
ovules  arise  as  minute  protuberances  at  some  part  of  the  ova- 
rian wall  or  upon  the  axis  of  the  ovary.     In  orchids  the  pro- 
tuberance consists  of  only  a  single  row  of  cells ;  but  in  most 

1  Morren.  a  Gardeners'  Chronicle,  1846,  p.  771. 

3  Kolreuter  :  Vorlaufige  Nachricht  (quoted  by  Balfour :  Class  Book  of 
Botany,  p.  564). 

*  Gartner  :  Beitrage  zur  Kenntniss,  p.  346  (quoted  by  Darwin  in  "Effects 
of  Cross  and  Self  Fertilization  in  the  Vegetable  Kingdom,"  p.  377). 

The  following  are  some  of  Hassall's  determinations  of  the  number  of  pollen- 
grains  (Annals  of  Nat.  Hist,  viii.,  1842,  p.  108):  Dandelion,  243,600  grains  ; 
a  flower  of  Peony,  with  174  stamens  each  containing  21,000  pollen-grains, 
3,654,000  ;  while  in  a  plant  of  Rhododendron  the  number  of  grains  was  esti- 
mated to  be  72,620,000. 


STRUCTURE   OF  THE   OVULE. 


433 


other  cases  several  rows  of  cells  are  superposed,  forming  the 
body  known  in  morphology  as  the  nucleus  of  the  ovule.  This, 
to  avoid  the  possibility  of  even  slight  confusion,  will  be  now 
spoken  of  as  the  nucellus. 

That  this  distinction  is  necessary, 
will  appear  from  the  fact  that  in  one 
of  the  large  cells  of  this  body  there 
is  a  true  cell-nucleus  which  under- 
goes remarkable  changes,  all  of  which 
must  be  described.  It  should  there- 
fore be  remembered  that  in  the  fol- 
lowing discussion  the  term  nucellus 
means  exactly  that  which  in  Volume 
I.  page  277  is  called  nucleus  of  the 
ovule. 

1125.  Around  the  nucellus  there  is  developed  in  most  in- 
stances a  double  ring,  which  soon  nearly  invests  it,  forming  an 

inner  and  an  outer  coat.  Attention 
has  been  called  in  Volume  I.  to  the 
fact  that  the  integuments  of  the  ovule 
do  not  complete!}-  invest  the  nucel- 
lus, but  that  there  is  at  its  true  apex 
an  orifice  known  as  the  foramen  or 
micropyle.  It  has  also  been  shown 
that  by  a  peculiar  distortion  during 
its  development  the  ovule  may  be 
so  bent  round  upon  its  support,  the 
funiculus,  as  to  have  the  micropyle 
present  itself  towards  the  placental 
attachment.  Hence,  when  the  apex 
of  the  ovule  is  spoken  of,  the  micro- 
pylar  extremity  is  meant. 

1126.  At  the  micropylar  extremity  of  the  forming  ovule,  a 
single  cell,  beneath  the  surface  (except  in  orchids  and   some 
saprophytes) ,  elongates  in  the  direction  of  the  length  of  the  ovule, 
and  by  one  or  sometimes  many  transverse  and  vertical  partitions 
becomes  divided  into  segments  of  unequal   size.     The  lowest 
segment  continues  the  elongation  and  the  enlargement  of  the 
structure  thus  formed  within  the  ovule,  known  as  the  embryo 


FIG.  197.  Longitudinal  section  of  the  amphitropous  ovule  of  Baptisia  australia. 
(Van  Tieghem.) 

FIG.  198.  Longitudinal  section  of  the  anatropous  ovule  of  Mimosa  pudica.  (Van 
Tieghem). 


434 


KEPRODtTCTION. 


sac.  During  the  subsequent  development  of  the  ovule  the 
embryonal  sac  continues  to  increase  in  size,  often  irregularly, 
and  displaces  or  obliterates  by  absorp- 
tion mairy  of  the  cells  around  it. 

1127.  At  an  early  period  in  the  de- 
velopment of  the   embryonal   sac   it  is 
completely   filled   with   protoplasm   con- 
taining a  cell-nucleus.     This  nucleus  di- 
vides, and  the  two  new  nuclei  are  soon 
found  at  opposite  ends  of  the  sac,  where 
each  divides  into  four  nuclei.     Between 
the  two  groups  of  four  nuclei  there  may 
be  a  vacuole  of  considerable  size. 

The  next  stage  is  marked  by  the  pas- 
sage of  a  nucleus  from  each  extremity  of 
the  embryonal  sac  towards  its  centre, 
where  they  become  united  to  form  a  sec- 
ondary  nucleus. 

1128.  The  nuclei  at  the  lower  end  of 
the  sac  become   surrounded   with  other 

protoplasmic  matter,  and  later  by  cell-walls ;  they  then  consti- 


tute what  have  been  termed  the  antipodal  cells.     At  the  tipper 
end  of  the  sac,  also,  the  three  nuclei  become  surrounded   by 

FIG.  199.  Longitudinal  section  of  theorthotropous  ovule  of  Polygonum  divaricatum. 
fu,  fnniculus;  te,  the  two  Integuments;  MM,  the  nucellus,  whose  summit  is  prolonged 
towards  the  micropyle,  mi ;  se,  the  embryonal  sac.  (Strasburger.) 

Fro.  200.  Polygonum  divaricatum.  Summit  of  the  ovule  with  the  apex  of  the  em- 
bryo sac,  and  the  complete  embryonal  apparatus,  e,  the  oospore;  »,  one  of  the  syner- 
gldae,  the  other  being  hidden  from  view.  (Strasburger.) 

FIG.  201.  Polygonum  divaricatum.  Summit  of  the  ovule,  showing  the  encroachment 
of  the  embryo  sac  upon  the  adjoining  cells.  (Strasburger.) 


CHANGES   IN   THE   OOSPHERE. 


435 


more  or  less  pi'otoplasmic  matter,  but  are  not  invested  by  a 
true  cell-wall ;  these  have  been  termed  the 
egg-apparatus.  Two  of  these  naked  nu- 
cleated bodies  are  somewhat  attenuated  at 
their  upper  part  and  rounded  below ;  the 
slender  portion  contains  the  nucleus,  the 
rounded  a  vacuole.  The  bodies  are  termed 
the  synergidce.  The  remaining  cell  is  near 
the  lower  extremity  of  the  two  just  de- 
scribed, and  is  known  as  the  odsphere. 
All  of  these  parts  are  shown  in  the  fig- 
ures. 

Such,  then,  is  the  structure  of  the  em- 
bryonal sac  and  of  the  egg-apparatus, 
when  the  extremity  of  the  pollen-tube 
emerges  into  the  cavity  of  the  ovar}7  and 
comes  in  contact  with  the  micropj'le,  or 
foramen.  It  has  been  shown  by  Stras- 
burger,  that  when  contact  takes  place  be- 
tween the  pollen-tube  and  the  summit  of 
the  embryonal  sac,  one  of  the  synergidae 
changes  its  character ;  its  rather  clear  pro- 
toplasm becomes  turbid,  its  vacuole  and 

nucleus  vanish,  and  with  a  slight  con- 
traction the  mass  becomes  finely  granu- 
lar, after  which  it  rna\-  wholly  disappear. 
At  this  time  the  ob'sphere  also  undergoes 
the  following  changes :  it  clothes  itself 
with  a  thin  film  of  cellulose,  and  in  its 
protoplasmic  mass  a  well-marked  nucleus, 
probably  derived  as  such  from  the  pollen- 
tube,  appears  by  the  side  of  the  nucleus 
of  the  oosphere,  sometimes  of  the  same 
size,  sometimes  smaller.  The  two  nuclei 
blend,  forming  a  single  ovoid  body,  with 
distinct  or  with  confluent  nucleoli.  Even 
if  at  first  distinct  the  nucleoli  may  be- 
come confluent  at  a  later  period.  The 

FIG.  202.  Synergidse  prolonged  across  the  membrane  of  the  embryonal  sac.  a,  b,  c, 
from  Gladiolus  cominunis ;  d,  from  Bartonia  aurea.  a,  plane  perpendicular  to  the 
plane  of  the  symmetry  of  the  ovule  ;  b,  in  the  plane  of  symmetry  ;  c,  after  separation  of 
the  three  parts ;  d.  (Strasburger.) 

FIG.  203.  Capsella  Bursa-pastoris.  Two  embryos  with  cotyledons  distinctly  devel- 
oped. B  more  advanced  than  A.  (Luerssen.) 


REPRODUCTION 


other  synergide  remains  unchanged,  or 
passes  through  nearly  the  same  changes 
as  those  described.  It  should  be  said 
that  in  some  instances  the  pollen-tube 
passes  down  without  apparently  affect- 
ing the  synergidae  to  any  very  marked 
extent,  but  producing  its  influence  di- 
rectly upon  the  oosphere. 

1129.  These  changes  now  described 
in  the  oosphere  are  known  collectively 
as  those  of  fertilization  or  impregnation  ; 
the  fertilized  or  impregnated  oosphere 
is  termed  an  oospore.  It  passes  through 
a  series  of  changes  b}-  which  a  second 
cell  is  formed,  then  others  in  a  linear 
series,  or  in  a  more  complex  chain, 
termed  the  proembryo  or  suspensor. 
In  some  cases,  however,  no  suspensor 
at  all  is  produced. 


FIG.  204.  Capsella  Bursa-pastoris.  Embryo  developed  more  than  In  Fig.  203.  A 
longitudinal  section  showing  cotyledons,  kb  ;  r,  point  of  growth;  e,  suspensor ;  pi, 
plerom  ;  p  and  pe,  periblem  ;  rf,  and  rf2,  dermatogen;  A>,  and  h*.  root-cap.  (Hanstein.) 

FIG.  205.  Camelina  sativa.  o,  two-celled  embryo,  much  exceeded  In  size  by  the 
long  suspensor.  Capsella  Bursa-pastoris,  the  figures  l>,  r,  showing  different  stages  in  the 
development  of  the  embryo;  b,c,  d,  aspects  of  the  embryo  divided  into  quadrants;  e,f,g, 
different  views  of  the  embryo  at  the  formation  of  the  dermatogen  ;  i,  longitudinal  sec- 
tion showing  further  divisions  and  the  formation  of  the  periblem  and  plerom;  k,  same 
as  t,  but  given  in  perspective;  I,  longitudinal,  m,  transverse,  section  of  the  same  em- 
bryo at  a  later  stage ;  n,  perspective  view  of  embryo  at  a  little  earlier  stage  than  /  and 
m ;  o,  p,  r,  later  stages;  </,  same  embryo  seen  from  below,  exhibiting  the  first  divisions 
near  the  suspensor;  «,  «',  a",  cells  nearest  the  suspensor.  (Luerssen,  after  Praz- 
mowski.) 


FERTILIZATION  IN  GYMNOSPERMS. 


437 


1130.  The  terminal  cell  of  the  suspensor  is  followed  by  the 
initial  cell  or  cells  of  the  embryo  proper ;  the  different  stages  of 
the  development  of  the  embryo  can  be  traced  in  the  ovule  of  one 
of  our  most  common  weeds,  Capsella  (compare  Figs.  203-205). 

The  case  above  described  is  a  simple  one,  but  may  serve  as  a 
type  of  all  normal  cases  of  fertilization  in  angiosperms,  the  innu- 
merable deviations  from  which  cannot  be  further  alluded  to  here.1 

1131.  With  the  changes  in  the  embryo  sac  there  are  concomi- 
tant changes  in  the  whole  nucellus  and  its  integuments.     A 
certain  amount  of  food  of  some  kind  (see  509)  is  stored  either 
in  the  sac  or  in  the  developing  tissues  around  it,  constituting 
the  so-called  albumen  of  the  seed.     The  food  within  the  develop- 
ing embryo  sac  is  termed  endosperm  ;  if  around  it,  perisperm. 
But   the   changes   do    not    stop   with   the    ovule    as    it   ripens 
into  a  seed ;    they  go  on   also  in   the  surrounding  parts.      In 
fact,  as  soon  as  fertilization  has  begun,  the  flower  wilts,  and 
in  most  cases  the  external  organs  fall.     The  ovary,  sometimes 
with  associated  parts  such  as  the  calyx,   the  receptacle,  etc., 
passes  through  changes  by  which  it  becomes  the  fruit. 

FERTILIZATION  IN  GYMNOSPERMS. 

1132.  The  chief  differences  between  the  reproduction  in  these 
plants  and  that  in  those 

just  described  are  in  the 
preliminary  development 
of  the  pollen  and  the 
ovule. 

1133.  Pollen  of  gym- 
nosperms.      The    grain 
is  distinctly  divided  b}- 
a  curved  partition  into 
two  portions,  and  one  of 
these    portions    is    fre- 
quently divided  in  much 
the  same  way  into  two 
parts.      Comparison    of 
this  pollen  with  that  of 

-  The  student  is  urged  to  study  with  great  care  the  masterly  treatise  by 
Strasburger,  Ueber  Befruchtung  und  Zelltheilung,  1878,  and  the  more  succinct 
account  in  his  Practicum,  1884. 

FIG.  206.  A,  pollen-grains  of  Biota  before  their  escape  from  the  pollen-sac.  7,  fresh, 
77  and  III  swollen  by  water;  the  extine  e  having  split  off,  the  protoplasmic  contents 
are  seen.  B,  pollen-grains  of  Pinus  pinaster  before  their  escape  from  the  pollen-sac;  a 
side  and  a  dorsal  view.  (.Sachs.) 


438 


REPRODUCTION. 


angiosperms  shows  that  in  the  latter  the  nucleus  divides,  but 
that  the  division  stops  here,  no  true  dividing-wall  being  formed. 

1134.  Ovule  of  yymnosperms.  The 
ovule  is  alwa3's  orthotropous.  It  has  an 
integument  which  is  sometimes  prolonged 
so  as  to  form  a  fleshy  tube  communicating 
with  the  nucellus. 

The  nucellus,  like  that  of  angiosperms, 
contains  an  embryonal  sac ;  at  an  earty 
stage  this  is  filled  with  endosperm,  which 
it  will  be  remembered  is  not  developed  in 
angiosperms  until  after  fertilization.  Some 
of  the  upper  cells  of  the  endosperm  are 
rather  larger  than  the  others,  elongated  in 
the  direction  of  the  axis  of  the  ovule,  and 
each  surmounted  by  a  "  rosette  "  of  minute 
cells  which  comes  between  the  group  and 
the  summit  of  the  ernb^'o  sac.  These  large 
cells,  with  their  rosettes,  are  termed  cor- 

puscules.  These  corpuscules  are  considered  oospheres.  Around 
them  in  the  embryo  sac  there  ap- 
pears to  be  nothing  corresponding 
strictly  to  the  synergidae,  the  an- 
tipodal cells,  etc.,  observed  in  the 
angiosperms,  although  some  ho- 
mologies  have  been  pointed  out. 

In  some  cases,  like  that  figured, 
there  is  a  sort  of  depression  at 
the  summit  of  the  endosperm, 
which  has  been  called  the  pollinic 
chamber. 

1135.  Contact  of  pollen  with 
the  ovtile.  As  the  name  indi- 
cates, the  gymnosperms  are  naked 
seeded ;  no  stigma  or  style  inter- 
venes between  the  pollen  and  the 
ovule.  When  the  divided  pollen 
of  the  gymnosperm  falls  uppn  the  micropyle  of  the  ovule,  it 

FIG.  207.  Pollen-grain  of  Ceratozamia  longlfolia.  A,  grain  with  partial  partitions  ; 
B,  the  same  emitting  its  tube,  ps,  which  has  ruptured  the  outer  coat ;  y,  minute 
inactive  cells.  ( Juranyl.) 

FIG.  208.  Longitudinal  section  of  the  nucellus  of  the  naked  ovule  of  Juniperus 
Virginiana.  n,  micellns  :  KP,  membrane  of  the  embryonal  cac  ;  e,  endosperm ;  c,  cor- 
puscles ;  />,  a  pollen-grain  which  has  protruded  its  large  tube  as  far  as  the  corpuscles. 
(Strasburger.) 


FERTILIZATION    IN   GYMNOSPERMS. 


439 


finds  there  a  certain  amount  of  moisture  b}*  means  of  which  a 
tube  is  formed  from  one  of  the  large  cells.  This  extends  directly 
into  the  tissue  of  the  nucellus,  coming  sooner  or  later  into  con- 
tact with  the  summit  of  the  embryonal  sac,  and  then  affecting 
the  corpuscules  below.  From  the  fertilized  corpuscule  the  embryo 
is  developed.1 


*  For  the  purpose  of  affording  some  means  of  comparison  of  the  methods  of 
reproduction  in  flowering  plants  and  in  those  of  a  lower  grade,  the  following 
brief  notes  concerning  the  reproduction  in  several  of  the  groups  of  Cryptogams 
have  been  inserted :  — 

(1)  No  sexual  reproduction  has  yet  been  demonstrated  in  the  very  lowest 
forms  of  vegetation.     Such  plants  are  termed  Protophytes.     The  fungi  which 
are  associated  with  fermentation  and  putrefaction,  and  certain  of  the  simplest 
alga;,  are  examples  of  the  group. 

In  the  study  of  the  Protophytes  the  beginner  can  examine  with* profit  the 
cells  of  common  yeast.  Care  should  be  taken  to  distinguish  between  the  cells 
of  the  plant  and  the  grains  of  starch  with  which  compressed  yeast  is  generally 
associated. 

The  simple  one-celled  plants  with 
chlorophyll  which  belong  to  this  group 
can  be  found  in  almost  any  stagnant 
water.  They  are  spherical,  and  are  fre- 
quently grouped  in  twos  or  fours. 

( 2 )  The  sexual  process  in  Zygophy tes 
is  characterized  by  the  confluence  of  the 
protoplasmic  masses  of  two  very  similar 
cells  by  which  a  new  mass  is  formed 
as  the  starting-point  of  the  new  indi- 
vidual.    In    most  of  these  zygophytes 
there   is   no  plain    distinction   of   sex. 
Some  of  the   lower  moulds  and  many 
of  the  filamentous  algae  are   examples 
of  the   group. 

Excellent  specimens  for  study  may 
be  found  in  stagnant  or  slow-running 
water  in  spring  and  through  the  sum- 
mer. By  careful  search  it  is  possible 
to  detect  cases  in  which  the  process  of 
conjugation  has  advanced  somewhat : 
such  specimens  can  be  kept  under  ob- 
servation by  having  the  slide  sufficiently 
warm  and  constantly  supplied  with  fresh 

water,  when  the  different  stages  of  conjugation  and  of  cell-division  may  be 
examined. 

FIG.  209.  Spirogyra,  illustrating  the  mode  of  fertilization  in  the  Zygophytes. 
Approximating  cells  of  two  filaments  produce  extensions  which  become  conjoined  ;  the 
protoplasmic  masses  in  these  cells  become  confluent,  forming  a  single  mass  which  after 
escaping  becomes  clothed  with  a  cell-wall  and  develops  into  a  filamentous  chain  of 
cells.  In  this  case  there  is  no  appreciable  distinction  of  sex. 


440 


REPRODUCTION. 


1136.  It  was  formerly  thought  that  no  clear  gradations  could 
be  detected  between  the  flowering  plants  and  the  higher  groups 

(3)  Oophytes.     In  this  group  a  mass  of  protoplasm,  known  as  an  obsphere, 
is  fertilized  by  specialized  threads  or  slender  masses  of  protoplasmic  matter 

termed  antherozoids,  coming 
from  another  part  of  the 
same  or  of  another  plant. 
By  contact  with  these  an- 
therozoids the  oosphere  be- 
comes an  obspore,  the  start- 
ing-point of  a  new  individual. 
In  this  group,  of  which 
Fucus  or  rock -weed  may  lie 
taken  as  an  example,  the 
fertilization  is  direct. 

In  the  examination  of  this 
group  the  student  may  em- 
ploy the  common  rock-weed 
which  carpets  the  boulders 
along  the  coast.  Sections 
should  be  made  in  the  un- 
even pustulated  part  of  the 
f  "jgf»*i  frond,  and  in  a  vertical  di- 

c\     Nix'    -/          HHU  rection.     Good  preparations 

can  be  obtained  from  mate- 
rial  which  has  been  dried  or 
from  that  which   has   been 
kept  in  alcohol,  and  winter  specimens  will  be  found  esj)ecially  good. 

Some  of  the  species  are 
dioscious,  having  the  male 
elements  in  the  conceptacles 
on  one  plant  and  the  female 
elements  in  those  upon  an- 
other. 

(4)  Carpophytes.      The 
simplest  plants  of  this  het- 
erogeneous group  are  illus- 
trated by  Fig.  211.     The 
oosphere  is  contained  in  a 
specialized  organ  (the  car- 
pogonium),    which    is    fre- 
quently prolonged  to  form 
a  style-like  process  (the  tri- 
chogyne).    The  antherozoids 

are  carried  by  water  to  this  process,  and  fertilization  results ;  the  product  of 
PIG.  210.  Fucus,  illustrating  the  fertilization  of  an  oophyte.  a,  section  through  a 
conceptacle  exhibiting  the  reproductive  organs;  b  and  c,  the  oospheres  in  different 
stages  of  development;  d,  antheridia  with  a  single  antherozoid  (</);  e,  an  oosphere 
surrounded  by  antherozoids ;  /,  an  oosphere  germinating.  (Thuret  ) 

PIG.  211.  Nemalion.  I.-IV.,  a  carpophyte.  I.,  a  branch  showing  antheridia,  o,  and 
a  carpogonium,  o,  with  the  trichogyne,  t  (e,  spermatium).  V.,  Lejolisia  exhibiting  a,  an- 
theridium,  c,  carpogonium,  and/,  ripe  fruit  j  e,  an  escaping  spore.  (Thuret  and  Bornet.) 


REPRODUCTION   IN   CRYPTOGAMS. 


441 


of  flowerless  plants.     Comparative  investigations  have,  however, 
shown  that  such  gradations  do  exist,  and  that  the  chain  of  exist- 


fertilization  is  shown  in  the  figure.  Of  the  more  complicated  cases  this  is  not 
the  place  to  speak  ;  their  treatment,  as  well  as  that  of  all  the  simpler  forms, 
may  be  looked  for  in  Volume  III. 

Specimens  for  this  demonstration  of  the  different  stages  of  reproduction  are 
to  be  procured  at  different  seasons.  As  will  be  seen  from  the  figure,  most  of 
the  features  are  so  nearly  superficial  as  to  need  no  particular  sections  for  their 
exhibition. 

(5)  True  mosses  and  their  allies  are  characterized  by  the  possession  of  an 
archegonium  or  flask-shaped  body  containing  a  central  cell  in  which  is  the 
oosphere.  The  ob'sphere  is  fertilized  by  immediate  contact  with  antherozoids 
which  are  formed  in  antheridia ;  as  a  result  of  the  fertilization,  there  is 
produced  a  spore-case  filled  with  spores. 

In  the  examination  of  the  fructification  of  a  moss,  the  plant  must  be  taken 
at  an  early  stage,  and  search  must  be  made  for  the  sexual  organs  by  removal  of 
the  flower-like  cluster  of  leaves 
at  the  summit  of  the  minute 
stalk.  If  the  removal  is  success- 
fully performed,  and  the  plant  is 
in  the  right  condition,  a  group 
of  threads  like  those  shown  in 
the.  figure  will  be  plainly  seen. 
Among  these  are  to  be  found 
some  flask-like  bodies,  the  arche- 
gonia,  and  either  on  the  same 
receptacle  or  on  another  plant 
of  the  same  species  the  male 
organs,  one  of  which,  greatly 
magnified,  is  shown  in  Fig.  212. 
Under  a  very  high  power  the 
escaping  antherozoids  can  be 
seen.  When  fertilization  has 
taken  place,  the  archegonium 
goes  on  in  its  development,  be- 
coming, after  many  intermediate 
steps,  the  capsule  or  "fruit"  of 
the  moss,  covered  by  a  sort  of 
hood  or  cap,  and  tightly  closed 
at  its  month  by  a  lid.  Removal 
of  the  lid  discloses  the  teeth  of 
the  mouth  (peristome)  and  the 
spores  within.  Upon  germina- 
tion, a  spore  gives  rise  to  slender 
filaments  among  which  is  pro- 
duced the  minute  moss-plant  with  the  sexual  organs  figured  in  the  sketch. 

PIG.  212.  Punaria  hygrometrica,  a  moss.  1.  Longitudinal  section  through  the 
upper  part  of  the  plant  with  archegonia,  a,  and  leaves,  b.  2.  Antheridium  bursting 
and  allowing  escape  of  the  antherozoids,  a.  (Thome.) 


442 


REPRODUCTION. 


ences  is  practically  unbroken,  reaching  from  the  lowest  to  the 
highest  forms.  The  character  of  this  evidence  will  appear  in 
the  succeeding  volume  of  this  series. 


(6)  True  ferns  exhibit  the  following  phenomena  of  fertilization.  On  the 
back  of  the  frond  there  are  formed  spores  in  spore-cases,  which  are  variously 

grouped  and  protected. 
The  spores  on  reaching 
a  fit  surface  soon  give 
rise  to  thin  films  (pro- 
thalli),  on  the  under 
side  of  which  are  pro- 
duced the  sexual  or- 
gans, all  of  which  are 
shown  in  the  figures. 
As  a  result  of  the  pro- 
cess of  fertilization  there 
is  produced  afern-plant, 

W  which  at  its  adult  age 

bears  the  spores  above 
spoken  of. 
In  any  greenhouse 
where  ferns  are  kept  it 
is  easy  to  procure,  by 
careful  search  on  the 
soil  of  the  flower-pots, 
abundance  of  the  pro- 
thalli  in  different  stages. 
The  most  minute  of 
these,  exhibit  the  sexual 
organs  just  forming, 
while  those  which  are 
more  advanced  give  all 
the  features  shown  in 
the  figures.  The  stu- 
dent must  observe  that 
on  the  surface  of  the  soil 
in  the  flower-pots  many 
other  growths  are  to  lie 
found,  and  care  must 
be  taken  not  to  con- 
found other  flat  films 
(belonging,  for  in  stance, 
to  Hepaticae)  with  the 
prothalli  of  the  ferns. 

Sections  through  the  prothallus  will  exhibit  the  sexual  organs  in  different 
stages  of  development.  The  best  material  is  procured  by  the  cultivation  of 

FIG.  213.  Prothallus  of  a  fern,  exhibiting  the  reproductive  organs.  At  the  sinus 
of  the  heart-shaped  film  are  to  be  seen  the  archegonia,  one  of  which,  more  highly  mag- 
nified, Is  displayed  In  section  In  A.  £,  an  enlarged  antheridium  with  escaping  authero- 
zoida.  (Luerssen.) 


SEXUAL   AND   NON-SEXUAL  REPRODUCTION. 


443 


1137.  Contrast  between  non-sexual  and  sexual  reproduction  as 
regards  results.  In  non-sexual  reproduction  a  certain  portion 
of  living  matter  is  separated  from  the  rest  of  the  living  matter 
of  the  plant,  and,  coming  under  favorable  conditions,  pursues 
an  independent  existence  ;  in  sexual  reproduction,  two  portions 
of  living  matter,  from  different  parts  of  the  organism  or  from 
different  organisms,  unite  to  constitute  a  new  individual. 


fern-spores.  On  a  piece  of  unglazed  earthenware,  for  instance  a  broken  flower- 
pot, which  has  been  first  boiled  for  a  time  in  water  to  destroy  any  injurious 
moulds,  a  few  spores  are  to  be  lightly 
dusted.  If  the  whole  is  covered  by  a 
bell-jar  and  kept  dark  and  warm,  after 
a  certain  time  the  delicate  films  will  be 
detected  and  can  then  be  traced  through 
their  development. 

(7)  Some  of  the  allies  of  the  ferns 
produce  spores  of  more  than  one  sort, 
differing  in  size  and  subsequent  devel- 
opment. The  larger  spores,  known  as 
macrospores,  give  rise  to  an  included 
prothallus  which  subsequently  becomes 
exposed  at  one  portion,  where  there  is 
developed  an  archegonium  (or  sometimes 
more  than  one).  Previous  to  or  coin- 
cident with  this  development  there  is 
formed  within  the  spore-walls  a  peculiar 
tissue  which  has  been  termed  the  endo- 
sperm, and  which  is  regarded  as  the 
homologue  of  the  endosperm  in  gymno- 
spermous  seeds.  The  smaller  spores  are 
denominated  microspores,  and  pursue  a 
peculiar  course  of  development.  One 
of  the  cells  (seldom  more  than  one) 
remains  essentially  unchanged,  while 

the  others  give  rise  to  the  mother-cells  of  the  antherozoids.  It  is  therefore 
thought  proper  to  consider  the  sterile  cell  as  the  homologue  of  a  rudimentary 
male  prothallus,  and  the  others  of  rudimentary  antheridia.  From  the  mother- 
cells  are  produced,  sooner  or  later,  the  antherozoids  by  which  the  archegonium 
is  fertilized. 

If  these  allies  of  the  ferns  are  compared  with  the  angiosperms,  wide  differ- 
ences are  found  to  exist  which  can  be  bridged  over,  in  part  at  least,  by  the 
gymnosperms.  Hence,  in  some  systems  of  classification  the  gymnosperms  are 
placed  between  the  angiosperms  and  cryptogams  instead  of  between  the  mono- 
cotyledons and  dicotyledons. 

Fig.  214.  Selaginella.  A,  F,  microspores  in  different  stages  of  formation  of  the 
antheridia  G,  antherozoid;  H,  axile  longitudinal  section  of  a  macrospore  six  weeks 
after  fertilization,  but  before  germination;  v,  rudimentary  prothallus  of  the  micro- 
spore  ;  p,  prothallus  of  the  macrospore  with  three  archegonia ;  end,  endosperm ;  e, 
exosporium.  (Pfefier.) 


444  REPRODUCTION. 

1138.  The  new  individual,  for  instance  a  bud,  arising  from 
non-sexual  reproduction,  generally  repeats  in  itself  all  the  pecu- 
liarities of  the  organism  from  which  it  took  its  origin  ;   the  new 
individual,  the  seed  or  spore,  arising  from  sexual  reproduction, 
usually  differs  in  some  particulars  from  the  organism  or  organ- 
isms by  which  it  was  produced. 

1139.  Hence,  in  the  higher  plants  individual  peculiarities  are 
perpetuable  by  bud- reproduction,  whereas  the  seed  gives  rise  to 
variations.     If  the  horticulturist  wishes  to  keep  the  descendants 
of  a  given  stock  true  to  all  the  characters  which  give  them  value, 
he  relies  upon  some  method  of  multiplying  the  plant  b}*  buds ; 
if,  on  the  contrary,  he  desires  to  induce  or  increase  some  varia- 
tion from  the  stock,  he  makes  use  of  seeds. 

1140.  The  ordinary  horticultural  operations  by  which  buds  are 
severed  from  the  parent  stock  and  suitably  placed  for  further 
advantageous  development  are  :   (1)  layering,  —  the  fastening  a 
branch  in  earth,  so  that  while  yet  connected  with  its  main  stem 
it  may  form  new  roots  and  afterwards   live  independently  of 
the  stem ;    (2)  the  forcing  of  cuttings  or  slips,  which  in  con- 
genial soil  will  produce  a  supply  of  roots ;   (3)  grafting,  or  the 
transfer  of  a  shoot  (a  scion)  from  the  parent  plant  to  some  other 
plant  by  which  it  can  be  nourished  ;  (4)  budding,  the  transfer  of 
a  single  bud  to  another  plant  (see  426). 

1141.  While  in  most  cases  buds  produce  shoots  or  plants  very 
closely  resembling  the  parent,   it  sometimes  happens   that  re- 
markable variations  arise.     These  are  known  as  bud-variations, 
and  are  commonly  called  sports.     In  general,  when  once  origi- 
nated they  are  perpetuable   by  any  of  the  processes  of  bud- 
propagation  just  described,  but  are  not  likely  to  be  reproduced 
by  seed.     From  the  long  list  of  them  given  by  Darwin  only  a 
few  familiar  cases  are  here  mentioned:  (1)  the  moss-rose,  from 
the  Provence  rose  (Rosa  ceutifolia)  ;   (2)   Pelargonium,  giving 
rise  to  numerous  varieties ;  (3)  Dianthus,  Sweet  William,  Car- 
nations, and  Pinks,  which  vary  very  widely  in  cuttings  from 
a  single  plant. 

1142.  Many  of  the  cases  of  sports,  especially  those  which  have 
descended  from  hybrids,  are  attributable  to  reversion  to  an  ances- 
tral form ;  a  few  seem  to  be  dependent  on  changes  in  the  sur- 
roundings ;  while  others  have  been  attributed  to  the  influence 
exerted  by  a  graft. 

1143.  Ordinarily  the  scion  produces  no  marked  effect  upon  the 
stock,  and,  conversely,  the  stock  exerts  no  effect  upon  the  shoot 
growing  from  the  scion.     But  when,  for  instance,  some  of  the 


CYTISDS  ADAMI.  445 

variegated  forms  of  Abutilon  have  been  grafted  on  green-leaved 
stocks,  they  have  been  known  to  affect  many  of  the  subsequent 
shoots.  Such  cases  are  known  as  graft-hybrids.  The  most 
remarkable  example  is  that  of  Cytisus  Adami,  a  form  midway 
between  Cytisus  laburnum  and  purpureus.  Of  this  plant  Darwin 
says  :  "  Throughout  Europe,  in  different  soils  and  under  different 
climates,  branches  on  this  tree  have  repeatedly  and  suddenly  re- 
verted to  both  parent  species  in  their  flowers  and  leaves. "  To 
behold  mingled  on  the  same  tree  tufts  of  dingy  red,  bright  yel- 
low,  and  purple  flowers,  borne  on  branches  having  widely  differ- 
ent leaves  and  manner  of  growth,  is  a  surprising  sight.  The 
same  raceme  sometimes  bears  two  kinds  of  flowers,  and  I  have 
seen  a  single  flower  exactly  divided  in  halves,  one  side  being 
bright  yellow  and  the  other  purple ;  so  that  one  half  of  the 
standard-petal  was  yellow  and  of  larger  size,  and  the  other  half 
purple  and  smaller.  In  another  flower  the  whole  corolla  was 
bright  yellow,  but  exactly  half  the  calyx  was  purple.  In  an- 
other, one  of  the  dingy-red  wing-petals  had  a  bright  yellow 
narrow  stripe  on  it ;  and  lastly,  in  another  flower  one  of  the 
stamens,  which  had  become  slightly  foliaceous,  was  half  yellow 
and  half  purple ;  so  that  the  tendency  to  segregation  of  char- 
acter or  reversion  affects  even  single  parts  and  organs.  The 
most  remarkable  fact  about  this  tree  is  that  in  its  intermediate 
state,  even  when  growing  near  both  its  parent  species,  it  is 
quite  sterile  ;  but  when  the  flowers  become  pure  yellow  or  pure 
purple  they  yield  seed."  Passing  over  the  views  expressed 
by  many  that  Cytisus  Adami  is  a  hybrid  produced  by  seed,  the 
account  of  its  origin,  quoted  by  Darwin,  is  here  given.  M. 
Adam  inserted  a  shield  of  Cytisus  laburnum  in  the  stem  of  C. 
purpureus ;  the  bud  lay  dormant  a  year  and  then  produced  a 
shoot  which  was  rather  more  vigorous  than  those  of  C.  purpureus ; 
this  shoot  was  propagated  and  the  plants  therefrom  were  sold  as  a 
variety  of  Cytisus  purpureus,  before  they  had  come  into  flower.1 

1  The  account  of  the  budding  was  published  after  they  had  flowered,  but 
before  this  extraordinary  tendency  to  reversion  had  been  manifested.  Upon 
a  review  of  the  testimony  Darwin  was  inclined  to  accept  the  foregoing  account 
of  the  origin  of  Cytisus  Adami  as  a  graft-hybrid  as  true.  Other  cases  are  to 
be  placed  in  the  same  category. 

For  a  full  statement  of  bud-variations  and  graft-hybrids  the  student 
should  read:  Darwin,  Variation  in  Animals  and  Plants  under  Domestication, 
1868,  vol.  1,  chap.  xi.  ;  also  Focke,  Die  Pflanzen-mischlinge,  1881,  p.  519. 
In  the  latter  is  an  interesting  account  of  the  mixed  oranges  (Bizarria).  Con- 
suit  also  Braun,  On  the  Phenomenon  of  Rejuvenescence  in  Nature  (Kay  Society, 
1853)  ;  and  numerous  papers  by  Caspary. 


446  REPRODUCTION. 

1144.  Apogamy.     The  prothallus  which  develops  from  a  fern- 
spore  bears  upon  its  under  side  the  sexual  organs ;  from  their 
interaction  a  bud  is  produced  which  grows  into  the  fern-plant. 
Farlow1  has  shown  that  in  some  cases  the  prothallus  can  give  rise 
to  a  bud  without  sexual  intervention.     De  Bary  2  has  traced  out 
the  connection  between  this  mode  of  budding  and  that  which  is 
found  in  certain  other  plants.     To  the  abnormal  budding  of  the 
prothallus  and  homologous  structures  he  has  given  the  name 
apogamy. 

1145.  Parthenogenesis8  is  the  production  of  an  embryo  with- 
out the  intervention  of  pollen  (or  the  equivalent  of  pollen  in  the 
lower  plants).     Coelebogyne  ilicifolia,  a  species  belonging  to  the 
order  Euphorbiacese,  has  been  known  to  produce  seeds  with  more 
than  one  embryo,  and  without  access  of  pollen.     It  has  been 
held  by  some  that  the  embryos  in  this  case  are  formed  from 
oospheres  which  had  not  been  fertilized,  but  investigations  by 
Strasburger  indicate  that  they  are  adventitious  outgrowths  from 
the  cellular  tissue  of  the  nucellus,  and  are  outside  of,  not  in,  the 
emb^o-sac. 

In  some  other  cases  examined,  Strasburger  regards  the  forma- 
tion of  embryos  outside  the  embryo-sac  as  dependent  upon  the 
fertilization  of  the  oosphere,  but  in  only  one  case  of  this  kind 
did  he  observe  any  embryo  form  also  from  the  fertilized  oospore. 

1146.  Polyembryony,  the  production  of  two  or  more  viable 
embryos  in  a  seed  after  the  manner  just  described,  is  of  frequent 
occurrence  in  oranges,  onions,  and  Funkia  (Day  Lily). 

1147.  Fertilization  in  different  degrees  of  consanguinity.    It  has 
been  shown  in  Volume  I.  that  "  no  two  individuals  are  exactty 
alike ;  and  offspring  of  the  same  stock  may  differ  (or  in  their 
progeny  may  come  to  differ)  strikingly  in  some  particulars.     So 
two  or  more  forms  which  would  have  been  regarded  as  wholty 
distinct   are   sometimes  proved   to  be  of  one   species   by  evi- 
dence of  their  common  origin,  or  more  commonly  are  inferred 

1  Quart.  Joura.  Mic.  Science,  xiv.,  1874,  p.  266  ;  Proceedings  Am.  Acad., 
ix.  p.  68. 

8  Botanische  Zcitung,  1878,  p.  449  et  seq. 

3  Braun:  Ueber  Parthenogenesis  bei  Pflanzen,  1857;  Hanstein  :  Die  Parthe- 
nogenesis der  Ccelebogyne  ilicifolia,  1877  ;  Hanstein  :  Botanische  Abhand- 
lungen,  1877  ;  Strasburger  :  Befruchtung  und  Zelltheilung,  1878. 

Cases  of  parthenogenesis  occur  in  the  lower  plants,  where  they  have  been 
followed  out  in  cultures  continued  for  a  considerable  time.  Their  consideration 
belongs  to  the  next  volume  of  this  series. 

For  an  account  of  parthenogenesis  in  animals,  see  Balfour  :  Treatise  on 
Comparative  Embryology,  1880  ;  also  Brooks  on  Heredity,  1883,  p.  55. 


CLOSE   AND    CKOSS   FERTILIZATION.  447 

to  be  so  from  the  observation  of  a  series  of  intermediate  forms 
which  bridge  over  the  differences.  Only  observation  can  inform 
us  how  much  difference  is  compatible  with  a  common  origin. 
The  general  result  of  observation  is  that  plants  and  animals 
breed  true  from  generation  to  generation  within  certain  somewhat 
indeterminate  limits  of  variation  ;  that  those  individuals  which 
resemble  each  other  within  such  limits  interbreed  freely,  while 
those  with  wider  differences  do  not.  Hence,  on  the  one  hand, 
the  naturalist  recognizes  Varieties  or  differences  within  the 
species,  and  on  the  other,  Genera  and  other  superior  associations 
indicative  of  remoter  relationship  of  the  species  themselves." 

"  Most  varieties  originate  in  the  seed,  and  therefore  the  foun- 
dation for  them,  whatever  it  may  be,  is  laid  in  sexual  reproduc- 
tion. .  .  .  Upon  the  general  principle  that  progeny  inherits  or 
tends  to  inherit  the  whole  character  of  the  parent,  all  varieties 
must  have  a  tendency  to  be  reproduced  by  seed.  But  the  in- 
heritance of  the  new  features  of  the  immediate  parent  will  com- 
monly be  overborne  by  atavism  ;  that  is,  the  tendency  to  inherit 
from  grandparents,  great-grandparents,  etc.  Atavism,  acting 
through  a  long  line  of  ancestry,  is  generally  more  powerful  than 
the  heredhy  of  a  single  generation.  But  when  the  offspring  does 
inherit  the  peculiarities  of  the  immediate  parent,  or  a  part  of 
them,  its  offspring  has  a  redoubled  tendenc}*  to  do  the  same,  and 
the  next  generation  still  more ;  for  the  tendencies  to  be  like  par- 
ent, grandparent,  and  great-grandparent  now  all  conspire  to  this 
result  and  overpower  the  influence  of  a  remoter  ancestry."  1 

1148.  The  reproductive  elements  in  a  complete  flower  may 
combine  to  produce  an  embryo.     In  this  case  the  pollen  and 
ovule  have  originated  upon  a  single  shoot,  within  very  narrow 
limits  of  difference  as  regards  the  time,  place,  and  conditions  of 
their  development,  and  the  result  of  their  union  is  what  might 
be  expected,  —  a  close  copy  of  the  parent  plant.     The  fecunda- 
tion of  a  flower  by  its  own  pollen  is  termed  close-fertilization,  or 
self-fertilization. 

1149.  In  cross-fertilization  the  pollen  fertilizing  the  ovule  of 
a  flower  comes  from  another  flower  of  the  same  species,  and  here 
the  reproductive  elements  have  been  developed  under  dissimilar 
conditions. 

1150.  In  hybridization  the  pollen  comes  from  a  flower  of  a 
different  species ;  and  in  this  case  the  conditions,  external  and 

1  Volume  I.  pp.  318,  319.  The  student  is  urged  to  review  carefully 
the  following  sections  also  in  that  volume  :  619  to  640,  and  657  to  662 
inclusive. 


448  REPRODUCTION. 

internal,  under  which  the  reproductive  elements  have  been  pro- 
duced are  widely  dissimilar. 

The  mechanism  by  which  close-fertilization  is  secured  in  some 
instances  and  absolutely  prevented  in  others  has  been  fully 
explained  in  Volume  I.  The  account  of  the  mechanism  is  now 
to  be  supplemented  by  a  statement  of  the  results  of  reproduction 
in  the  different  degrees  of  relationship. 

1151.  The  results   of  close-fertilization   contrasted  with  those 
of  cross-fertilization.     It  has  long  been  known  to  cultivators  of 
plants,  that  in  order  to  keep  the  desirable  varieties  which  are 
under  cultivation  "  true  to  seed  "  they  must  be  close  bred  ;  that 
is,  all  pollen  from  other  varieties  of  the  same  species  must  be 
excluded.     The  whole  subject  is  best  illustrated  by  reference  to 
the  numerous  experiments  by  Darwin  ;  the  exhaustive  nature  of 
which  is  indicated  by  an  account  of  a  single  series  given  nearly 
in  his  own  words. 

1152.  The  plants  experimented  upon  in  all  cases  were  raised 
from  carefully  ripened  seed,  and,  when  ready  to  flower,  were 
placed  under  nets  with  meshes  of  one  tenth  of  an  inch  in  diame- 
ter, in  order  that  all  pollen-carrying  insects  might  be  excluded. 

A  plant  of  Ipomcea  purpurea  (Morning  Glory),  growing  in  the 
greenhouse,  was  protected  in  the  manner  just  described,  after  ten 
of  its  flowers  had  been  fertilized  by  pollen  from  their  own  sta- 
mens, and  ten  others  by  pollen  from  a  distinct  plant  of  the  same 
species.  The  seeds  from  the  first  ten  flowers  may  be  termed 
self -fertilized,  those  from  the  other  ten,  crossed.  The  two  kinds 
of  seeds  were  placed  on  damp  sand  on  opposite  sides  of  a  glass 
tumbler  covered  by  a  glass  plate,  with  a  partition  between  the 
seeds,  and  the  glass  was  put  in  a  warm  place.  As  often  as  a  pair 
of  seeds  germinated  they  were  put  on  opposite  sides  of  a  pot, 
with  a  superficial  partition  between  them,  and  the  same  procedure 
was  followed  until  five  or  more  seedlings  of  exactly  the  same  age 
were  planted  on  the  opposite  sides  of  several  pots.  The  soil  in 
the  pots  in  which  the  plants  grew  was  well  mixed,  and  the  plants 
on  the  two  sides  were  always  watered  at  the  same  time  ;  thus  the 
seedlings  were  subjected  to  practically  the  same  conditions  from 
a  very  early  stage. 

In  the  same  manner  self-fertilized  and  crossed  seeds  were 
secured  during  ten  generations.  The  results,  so  far  as  these  can 
be  shown  by  measurement  of  the  plants,  are  exhibited  in  the 
following  table : 1  — 

i  Darwin  :  Effects  of  Cross  and  Self  Fertilization,  1876,  p.  52. 


CLOSE   AND   CKOSS   FEKT1L1ZAT1ON   CONTRASTED.      449 


IPOM<EA  PURPUEEA. 


1 

o£ 

*a 

ii 

"S"S 

^1| 

Number  of  the 
Generation. 

*! 

f| 

t*o   - 

^ 

»s 

flu 

iy 

2& 

M 
%<o~ 

11 

>.   *        •** 

till 

1*1* 

First  .... 

6 

86. 

6 

65.66 

100  :  76 

Second     .     .     . 

6 

84.16 

6 

66.33 

100  :  79 

Third.     .     .     . 

6 

77.41 

6 

52.83 

100  :  68 

Fourth     .     .     . 

7 

69.78 

7 

60.14 

100  :  86 

Fifth  .... 

6 

82.54 

6 

62.33 

100  :  75 

Sixth.     .     .     . 

6 

87.50 

6 

63.16 

100  :  72 

Seventh   .     .     . 

9 

83.94 

9 

68.25 

100  :  81 

Eighth     .     .     . 

8 

113.25 

8 

96.65 

100  :  85 

Ninth      .     .     . 

14 

81.39 

14 

64.07 

100  :  79 

Tenth      .     .     . 

5 

93.70 

5 

50.40 

100  :  54 

All  ten  generations 
taken  together. 

73 

85.84 

73 

66.02 

100  :  77 

1153.  The  results  of  close  and  cross  fertilization,  as  shown  by 
the  weight  of  the  seed-capsules,  are  given  by  Darwin  thus  :  "  The 
offspring  of  intercrossed  plants  of  the  ninth  generation,  crossed 
by  a  fresh  stock,  compared  with  plants  of  the  same  stock  inter- 
crossed during  ten  generations,  both  sets  of  plants  left  uncovered 
and  naturally  fertilized,  produced  capsules  by  weight  as  100 
to  51." l 


1  The  following  summary  (Darwin  :  Effects  of  Cross  and  Self  Fertilization, 
p.  56)  shows  more  of  the  results :  — 

First  generation  of  crossed  and  self-fertilized  plants  growing  in  competition 
with  one  another.  Sixty-five  capsules  produced  from  flowers  on  five  crossed 
plants  fertilized  by  pollen  from  a  distinct  plant,  and  fifty-five  capsules  pro- 
duced from  flowers  on  five  self-fertilized  plants,  fertilized  by  their  own  pollen, 
contained  seeds  in  the  proportion  of 100  to  93. 

Fifty-six  spontaneously  self-fertilized  capsliles  on  the  above  five  crossed 
plants,  and  twenty-five  spontaneously  self-fertilized  capsules  on  the  above  five 
self-fertilized  plants,  yielded  seeds  in  the  proportion  of  ...  100  to  99. 

Combining  the  total  number  of  capsules  produced  by  these  plants  and  the 
average  number  of  seeds  in  each,  the  above  crossed  and  self-fertilized  plants 
yielded  seeds  in  the  proportion  of 100  to  64. 

Other  plants  of  this  generation  grown  under  unfavorable  conditions  and 
spontaneously  self-fertilized  yielded  seeds  in  the  proportion  of   .     100  to  45. 
2P 


450  REPRODUCTION. 

1154.  "  All  the  self-fertilized  plants  of  the  seventh  genera- 
tion, and  I  believe  of  one  or  two  previous  generations,  produced 
flowers  of  exactly  the  same  tint ;    namely,  of  a  rich  dark  pur- 
ple.    So  did  all  the  plants,  without  any  exception,  in  the  three 
succeeding  generations  of  self-fertilized  plants ;  and  very  many 
were  raised  on  account  of  other  experiments  in  progress  not 
here  recorded.    .    .    .    The  flowers  were  as  uniform  in  tint  as 
those  of  a  wild  species  growing  in   a  state  of  nature.    .    .    . 
The  crossed  plants  continued  to  the  tenth  generation  to  vary- 
in  the  same  manner   as   before,   but  to   a   ranch   less   degree, 
owing  probably  to  their   having   become  more  or   less  closely 
inter- related."  1 

1155.  In  the  sixth  self- fertilized  generation  there  appeared  a 
plant  which  was  larger  than  its  crossed  competitor,  and  its  pow- 
ers of  growth  and  fertility  were  transmitted  to  its  descendants. 
Thus  it  appears  that  even  with  the  exclusion  of  foreign  pollen 
new  characters  can  assert  themselves. 

1156.  It  was  not  found  in  these  experiments  that  simply  cross- 
ing a  flower  from  another  flower  on  the  same  plant  was  produc- 
tive of  any  advantage  ;  on  the  contrary,  there  are  some  cases 
which  show  that  it  ma}7  result  in  an  actual  disadvantage.     "  The 
benefits  which  so  generall}'  follow  from  a  cross  between  two 

Third  generation  of  crossed  and  self -fertilized  plants.  Crossed  capsules  com- 
pared with  self-fertilized  capsules  yielded  seeds  in  the  ratio  of  .  100  to  94. 

An  e<[ual  number  of  crossed  and  self-fertilized  plants,  both  spontaneously 
self-fertilized,  produced  capsules  in  the  ratio  of  100  to  38.  And  these  capsules 
contained  seeds  in  the  ratio  of  100  to  94.  Combining  these  data,  the  produc- 
tiveness of  the  crossed  to  the  self-fertilized  plants,  both  spontaneously  self- 
fertilized,  was  as 100  to  35. 

Fourth  generation  of  crossed  and  self-fertilized  plants.  Capsules  from  flow- 
ers on  the  crossed  plants  fertilized  by  pollen  from  another  plant,  and  capsules 
from  flowers  on  the  self-fertilized  plants  fertilized  with  their  own  pollen,  con- 
tained seeds  in  the  proportion  of 100  to  94. 

Fifth  generation  of  crossed  and  self-fertilized  plants.  The  crossed  plants 
produced  spontaneously  a  vast  number  more  pods  (not  actually  counted)  than 
the  self-fertilized,  and  these  contained  seeds  in  the  proportion  of  100  to  89. 

Ninth  generation  of  crossed  and  self-fertilized  plants.  Fourteen  crossed 
plants  spontaneously  self-fertilized,  and  fourteen  self-fertilized  plants  sponta- 
neously self-fertilized,  yielded  capsules  (the  average  number  of  seeds  per  capsule 
not  having  been  ascertained)  in  the  proportion  of 100  to  26. 

Plants  derived  from  a  cross  with  a  fresh  stock  compared  with  intercrossed 
plants.  The  offspring  of  intercrossed  plants  of  the  ninth  generation,  crossed 
by  a  fresh  stock,  compared  with  plants  of  the  same  stock  intercrossed  during 
ten  generations,  both  sets  of  plants  left  uncovered  and  naturally  fertilized, 
produced  capsules  by  weight  as 100  to  51. 

i  Darwin  :  Effects  of  Cross  and  Self  Fertilization,  p.  59. 


NECTAR.  451 

plants  apparently  depend  on  the  two  differing  somewhat  in  con- 
stitution or  character.  .  .  .  The  mere  act  of  crossing  two  distinct 
plants  which  are  in  some  degree  inter-related  and  which  have 
been  subjected  to  nearly  the  same  conditions  does  little  good 
as  compared  with  that  from  a  cross  between  plants  belonging 
to  different  stocks  or  families  and  which  have  been  subjected  to 
somewhat  different  conditions."  1 

1157.  In  Volume  I.   the  different  methods  by  which  cross- 
fertilization  is  effected  were  sufficiently  described,  but  certain 
special  questions  were  then  purposely  left  unanswered  ;  namely, 
those  in  regard  to  the  anatomical  and  chemical  nature  and  the 
distribution   of  the  attractions  by  which  insects  are  allured  to 
flowers  to  insure  cross-pollination. 

1158.  The  nectar  which  certain  flowers  offer  to  insects  is  made 
known  by  color  or  odor,  or  both.     It  is  the  sweetish  liquid  com- 
monly called   the  "honey"  of  the  flower,  secreted  by  certain 
specialized  organs  known  as  nectar-glands.    Mention  has  already 
been  made  (453)  of  the  occurrence  of  these  glands  on  leaves. 
In  the  flower  they  consist  usually  of  specialized  parenchyma  not 
unlike   the   secreting  surface  of  the  stigma  (see    1109).     They 
are  sometimes  raised  by  a  stalk,  or  adenophore,  more  or  less 
above  the  surface   of  the   floral  organ  on  which  they  are  de- 
veloped, but  often  not  elevated  at  all. 

1159.  Nectar-glands  may  occur  upon  any  part  of  the  flower, 
upon  its  bracts,  or  even  upon  some  part  of  the  flower-stalk  near 
it.     The    "Cow-pea"  of  the  Southern  States   affords   a   good 
example  of  nectar-glands  on  the  flower-stalk.     Many  species  of 
Euphorbia  have  them   on  bracts ;    the  common  Passion-flower 
and  the  cotton  plant  of  the  South  also  have  them  on  the  same 
organs.    The  most  remarkable  case  of  arrangement  of  the  glands 
is  found  in  a  tropical  plant,  Marcgravia  nepenthoides ;  this  has 
been  thus  described :  "  The  flowers  are  disposed  in  a  circle, 
hanging  downwards  like  an  inverted  candelabrum.      From  the 
centre  of  the  circle  of  flowers  is  suspended  a  number  of  pitcher- 
like  vessels,  which,  when  the  flowers  expand  in  February  and 
March,  are  filled  with  a  sweetish  liquid.     This  liquid  attracts 
insects,  and  the  insects  numerous  insectivorous  birds.     The  flow- 
ers are  so  disposed,  with  the  stamens  hanging  downwards,  that 
the  birds  to  get  at  the  pitchers  must  brush  against  them,  and 
thus  convey  the  pollen  from  one  plant  to  another."  2 

1  Darwin  :  Effects  of  Cross  and  Self  Fertilization,  p.  61. 
3  Belt  ;  Naturalist  in  Nicaragua,  1874,  p.  128, 


452  REPRODUCTION. 

1160.  From  the  nectar-glands  of  proper  floral  organs  the  secre- 
tion of  nectar  is  generally  copious  and  is  prone  to  collect  in 
minute  cavities  such  as  shallow  pits,  or  in  conspicuous  special 
receptacles,  the  so-called  nectaries.     The  morphology  of  these 
organs  has  been  sufficiently  described  in  Volume  I.,  Chapter  VI. 

1161.  The  specific  gravity  of  nectar  is  very  variable.      The 
following  figures  are  from  Unger's l  determinations  :  — 

Agave  Americana 1.05 

"      geminiflora 1.09 

"      lurida 1.20 

If  it  is  assumed  that  the  solid  matter  in  nectar  is  wholly  sugar, 
these  figures  would  correspond  respectively  to  the  following 
amounts  of  cane-sugar ;  namely,  10,  18,  and  41.66  per  cent.2 

1162.  The  period  of  most  copious  secretion  of  the  nectar  usually 
coincides  with  the  maturity  of  the  anthers  or  of  the  stigma,  but 
in  some  cases  the  nectar  is  prepared  in  considerable  quantity 
before  the  flower  opens.8 

1163.  The  secretion  of  nectar  can  be  arrested,  as  Wilson  has 
shown,  by  carefully  washing  the  secreting  surface  with  a  jet  of 
water  and   then   drying  it  with   filter-paper.     Nectaries   which 
have  been  thus  made  inactive  through  removal  of  the  nectar  can 
be  again  brought  into  activity  by  adding  to  the  surface  a  little 
strong  syrup. 

1164.  The  secretion  from  nectar-glands  is  not  dependent  upon 
the  pressure  exerted  by  contiguous  cells.     When  the  flow  of  the 
nectar  from  a  nectar-secreting  surface  has  been  arrested  in  the 
manner  described  above,  a  pressure  of  even  40  centimetres  of 
mercury  upon  the  stem  is  insufficient  to  produce  any  effect ;  but 
the  activity  of  the  surface  is  at  once  resumed  when  a  little  syrup 
is  placed  upon  it. 

The  secretion  of  nectar  can  proceed  even  when  the  tissues  are 
not  turgescent.4 

1165.  The   colors  of  flowers  depend,   as   indicated  in  477, 
upon  the  existence  in  the  cells  of  minute  granules  or  of  colored 
sap.     The  shades  may  be  modified  to  some  extent  by  accidents 

1  Sitzungsberichte,  Berlin  Akademie,  xxv.,  1857,  p.  446. 

2  Wilson  :  in  Untersuchungen  aus  dem  bot.  lust.,  Tubingen,  1881,  p.  7. 

3  Bonnier  :  Les  nectaires,  Ann.  des  Sc.  nat.,  se"r.  6,  tome  viii.,  1879,  p.  5. 
*  For  details  see  an  important  memoir  by  Wilson  in  Untersuchungen  aus 

dem  bot.  Inst. ,  Tubingen,  1881,  i.  p.  1;  also  an  excellent  paper  by  Trelease, 
"  Nectar  and  its  Uses  "  (in  Report  on  Cotton  Insects,  U.  S.  Dept.  of  Agricul- 
ture, 1879),  which  contains  a  comprehensive  bibliography, 


COLORS   OF   FLOWERS. 


453 


of  surface  :  e.  g, ,  in  the  case  of  velvety  petals  the  color  is  often 
softened,  sometimes  to  a  remarkable  extent. 

1166.  Contrasted  colors  are  often  seen  in  a  single  flower.     In 
general  these  are  so  disposed  in  spots  or  lines  as  to  suggest  that 
they  bear  a  direct  relation  to  the  point  where  the  nectar  is  se- 
creted ;  hence  such  color-marks  were  called  by  Sprengel  nectar- 
spots  or  nectar-guides.    But  in  some  cases  flowers  have  conspicu- 
ous spots  without  being  nectariferous  ;  e.  g.  certain  poppies. 

1167.  Darwin  cites  the  following  case  as  showing  that  nectar- 
marks  have  been  developed  in  connection  with  the  nectaries: 
"  The  two  upper  petals  of  the  common  Pelargonium  are  thus 
marked  near  their  bases,  and  I  have  repeatedly  observed  that 
when  the   flowers  vary  so  as  to   become   peloric,  or  regular, 
they  lose  their  nectaries  and  at  the  same  time  the  dark  marks. 
When  the  nectar}7  is  only  partially  aborted,   only  one  of  the 
upper  petals  loses  its  mark.     Therefore  the  nectary  and  these 
marks  stand  in  some  sort  of  close  relation  to  one  another,  and 
the  simplest  view  is  that  they  were  developed  together  for  a 
special  purpose  ;  the  only  conceivable  one  being  that  the  marks 
serve  as  a  guide  to  the  nectary." l 

1 1 68.  The  colors  of  the  flowers  in  certain  species  change  more 
or  less  after  opening ;  thus  many  Borraginacese  turn  from  red 
to  blue  even  during  a  short  space  of  time.     One  of  the  most 
interesting  cases  of  this  change  of  color  is  presented  by  Arnebia. 
When  the  flower  opens  each  lobe  of  the  yellow  corolla  is  con- 
spicuously marked  by  a  deep  purple  spot ;  after  a  few  hours  this 
begins  to  fade,  and  by  the  next  day  entirely  vanishes. 

1169.  Of  all  colors  of  flowers  white,  pale  }rellow,  and  yellow2 
are  the  most  common. 

1  Effects  of  Cross  and  Self  Fertilization,  1876,  p.  373. 

2  The  following  table  by  Kohler  and  Schiibeler  (cited  by  Balfour)  exhibits 
the  relative  frequency  of  certain  colors  in  the  plants  of  twenty-seven  different 
families  of  plants  :  — 


Color  of  flower. 

In  4200  species. 

Mean  of  1000. 

White              .        .    . 

1193 

284 

Yellow 

951 

226 

Red 

923 

220 

Blue 

594 

141 

Violet  

307 

73 

Green       .         

153 

36 

Orange     
Brown  
Black  ... 

50 
18 
g 

12 
4 
2 

454 


REPRODUCTION. 


1 1 70.  The  colors  of  flowers  have  been  variously  classified  ;  thus 
De  Candolle  divides  them  into  a  xanthic  (3-ellow)  and  a  cyanic 
(blue)  series,  both  of  which  can  pass  into  red  and  white.     With 
few  exceptions,  these  two  series  are  not  represented  in  the  same 
blossom. 

1171.  The   odors   of  flowers   depend   in    some   cases    (e.  g. 
orange-blossoms)  upon  the  presence  of  a  volatile  oil  which  can 
be  extracted  by  distillation ;    but  in  many  other  instances  the 
odoriferous  principle  cannot  be  separated  by  chemical  or  other 
means. 

1172.  White  flowers  are  more  generally  fragrant  than  those 
of  any  other  color.     ';  The  fact  of  a  larger  proportion  of  white 
flowers  smelling  sweetly  may  depend  in  part  on  those  which  are 
fertilized  by  moths,  requiring  the  double  aid  of  couspicuousness 
in  the  dusk  and  of  odor.     So  great  is  the  economy  of  nature  that 
most  flowers  which  are  fertilized  by  crepuscular  or  nocturnal 
insects  emit  their  odor  chiefly  or  exclusively  in  the  evening."  1 


1  Darwin:  The  Effects  of  Cross  and  Self  Fertilization  in  the  Vegetable 
Kingdom,  1876,  p.  374. 

According  to  Kohler  and  Schiibeler  (cited  by  Balfour),  the  distribution  of 
odor  with  regard  to  color  is  as  follows  :  — 


Color. 

Species. 

Odoriferous. 

Odors 
agreeable. 

Odors 
disagreeable. 

White 

1193 

187 

175 

12 

Yellow     .         ... 
Red  
Blue     
Violet  
Green 

951 
923 
594 
807 
153 

75 
85 
31 
23 

61 

76 
23 
17 

14 

9 
7 
6 

orange     ...         .     . 
Brown      

50 
18 

3 
1 

1 

0 

2 

The  following  classification,  taken  partly  from  Trinchinetti,  as  cited  by 
Balfour,  indicates  the  diversity  which  exists  in  regard  to  the  periods  and  per- 
manence of  odors  of  flowers. 

(1)  Flowers  which  are  odoriferous  at  the  time  of  opening  and  which  remain 
so  throughout  ;  c.  g.  most  Roses. 

(2)  Flowers  in  which  the  intermission  of  odor  is  connected  with   their 
opening  and  closing  ;  and  in  this  class  there  are  two  subdivisions  :  — 

(a)  Those  which  are  closed  and  scentless  during  the  day,  and  are  open  and 
odoriferous  at  niglit. ;  e.  g.  Mirabilis  Jalapa,  Cereus  grandiflorus,  etc. 

(b)  Those  which  are  closed  and  scentless  at  night,  and  are  open  and  odor- 
iferous during  the  day  ;   e.  g.  Convolvulus  arvensis,    Cucurbita   Pepo,  some 
species  of  Nymphaea. 


HYBRIDS.  455 

1173.  Nectar  is  protected  in  various  ways  from  unwelcome 
insects  ;  that  is,  from  those  which  cannot  aid  cross-fertilization. 
The  chief  of  these  is  by  the  structure  of  the  flower  itself  or  the 
parts  below.     Characteristic  odors  and  certain  colors  ma}'  con- 
tribute to  this  protection.      Thus,  as  Muller  has  pointed  out, 
dull  yellow  flowers  are  entirely,  or  almost  entirely,  avoided  by 
beetles,  while  they  are  visited  by  Diptera  and  Hymenoptera 
(flies  and  bees). 

1174.  Hybrids  are  the  offspring  of  crossed  species.     But,  as 
shown  in  Volume  I.  page  320,  the  limits  which  separate  varie- 
ties from  species  are  sometimes  not  sharply  defined ;   hence  it 
happens  that  the  term  hybrid  has  been  also  applied  to  crosses 
between  strongly  marked  varieties  of  the  same  species.     Such 
offspring  should,  however,  be  termed  either  variety-hybrids  or 
cross-breeds,  and  the  word  hybrid  kept  to  its  proper  significa- 
tion. 

1175.  Wide  differences  exist  in  the  degrees  of  capacity  for 
producing  In'brids.     Thus  certain  closely  allied  species  cannot 
be  made  to  cross,  while  others  much  more  remote  in  apparent 
relationship  are  crossed  without  difficulty. 

1176.  In  general  the  limits  of  capacity  for  hybridizing  do  not 
extend  beyond  the  genus ;  a  few  cases,  however,  are  known  in 
which  species  usually  assigned  to  different  genera  have  been 
successfully  crossed.1     Hence  it  cannot  be  known  beforehand 
whether  the  attempt  to  cross  two  species  will  be  successful. 

(3)  Flowers  which  are  always  open,  but  which  are  odoriferous  at  one  time 
and  scentless  at  another.  Under  this  class  there  are  also  two  subdivisions  : 

(a)  Those  always  open,   and    only  odoriferous   during  the   day  ;    e.   g. 
Cestrum  diurnum,  Coronilla  glauca,  etc. 

(b)  Those  always  open,   and  only  odoriferous   at  night ;   e.  g.    Cestrum 
nocturnum,  Hesperis  tristis,  etc. 

In  certain  cases  odors  are  given  out  by  flowers  in  an  intermittent  manner. 
This  is  strikingly  shown  in  some  of  the  larger  night-flowering  species  of 
Cactaceae. 

Delpino  has  given  (Ulteriori  Osservazioni  sulla  Dicogamia  nel  Regno  Vege- 
tale,  1868-1874)  an  elaborate  classification  of  odors  as  they  exist  in  flowers. 
He  makes  forty-five  kinds  which  are  readily  distinguishable  as  peculiar,  while 
between  these  kinds  there  are  of  course  innumerable  gradations. 

1  Focke  notes  that  hybrids  between  species  belonging  to  different  genera 
are  comparatively  common  in  the  following  families  :  Caryophyllaceae,  Melas- 
tomaceaj,  Passifloracea?,  Cactaceae,  Gesneriacese,  Orchidacese,  Amaryllidacese, 
and  Gramineae ;  and  he  cites  also  the  following  instances  outside  of  these 
families  :  Brassica  X  Raphanus,  Galium  X  Asperula,  Centropogon  X  Sipho- 
campylus,  Campanula  X  Phyteuma,  Verbascum  X  Celsia,  Philesia  X  Lapageria. 
(Pflanzen-mischlinge,  1881,  p.  456). 


456  REPRODUCTION. 

1177.  In  reciprocal  hybridization  the  pollen  of  A  is  effective 
when  applied  to  the  stigma  of  JB  ;  and,  conversely,  the  pollen  of 
B  is  potent  when  applied  to  the  stigma  of  A.     But  it  sometimes 
happens  that  the  rule  will  not  work  both  ways.    Thus  the  pollen 
of  Mirabilis  longiflora  was  found  by  Kolreuter  to  produce  hybrids 
when  applied  to  the  stigma  of  Mirabilis  Jalapa  ;  but  the  pollen 
of  the  latter  was  without  effect  upon  the  stigma  of  the  former. 
Other  cases  are  known,  but  the  cause  of  this  extraordinary 
preference  is  not  understood. 

1178.  Hybrids  are   produced   artificially  by  the   transfer  of 
pollen  from  one  species  to  the  stigma  of  another  species,  care 
being  taken  to  exclude  all  pollen  of  the  second  species  from  its 
own  stigma.     The  pollen  is  best  transferred  by  means  of  a  sable 
or  camel's  hair  pencil.1      Exclusion  of  the  pollen  of  the  flower 
to  be  fertilized  must  be  secured  by  removal  of  the  anthers  before 
the  flower  opens.     This  is  easily  effected  by  the  use  of  delicate 
forceps,  an  incision  being  carefully  made  in  the  side  of  the 
corolla.     After  the  application  of  the  pollen  to  the  stigma,  the 
plant  or  blossom  must  be  covered  by  some  close  netting. 

1179.  Following  the  application  of  the  pollen,  changes  take 
place  in  the  fertilized  flower.     But,  as  Nageli  has  pointed  out, 
these  changes  in  many  cases  fall  far  short  of  yielding  satisfac- 
tory results  to  the  experimenter.    Nageli  describes  several  grades 
of  partial  fertilization:    (1)  that  in  which  the  ovary,  and  per- 
haps the  persistent  calyx,  grows  somewhat  without  appreciably 
affecting  the  ovules  ;    (2)  that  marked  by  greater  growth  of  the 
ovary,  and  by  slight  enlargement  of  the  ovules,  which  after- 
wards shrivel  up;    (3)  that  with  small  imperfect  fruits  with 
empty  seeds;    (4)  that  having  good  fruits  with  empty  seeds; 
(5)  that  with  normal  fruits  with  apparently  perfect  seeds  which 
have  no  germs  ;  (6)  that  producing  good  fruits  with  seeds  which 
have  only  minute  germs  incapable  of  further  development. 

In  successful  fertilization  there  are  produced  good  fruits  hold 
ing  sound  seeds. 


Some  of  the  cases  in  which  hybrids  have  been  produced  between  the 
species  of  different  genera  are  given  by  Nageli  (Sitz.  d.  k.  Akad.  d.  Wiss.  z. 
Munchen,  1865  and  1866),  as  follows  :  Rhododendron  and  Azalea,  Rhododen- 
dron and  Rhodora,  Rhodora  and  Azalea,  Rhododendron  and  Kalmia.  Of  those 
above  mentioned,  Rhododendron,  Rhodora,  and  Azalea  are  now  placed  by 
Bentham  and  Hooker  in  a  single  genus,  —  Rhododendron. 

1  It  is  of  great  importance  that  the  pollen  should  be  applied  at  exactly 
the  proper  period  for  impregnation.  This  is  usually  indicated  by  the  moisture 
of  the  stigmatic  surface. 


ARTIFICIAL   HYBRIDIZATION.  457 

1180.  If  to  a  stigma  pollen  from  two  species  is  applied  simul- 
taneously, only  that  will  be  potent  which  has  the  greatest  sexual 
affinity,  and  no  apparent  effect  will  be  produced  by  the  other. 

1181.  With  some  remarkable  exceptions,  hybrids  share  the 
general  characters  of  their  parents,  and  are  intermediate  between 
them.     It  sometimes  happens  that  part  of  the  offspring  of  a 
single  union  will  have  certain  characters,  while  the  rest,1  raised 
from  the  same  seed-pod,  will  possess  others. 

1  This  and  certain  other  points  referred  to  in  the  text  are  well  illustrated 
by  the  case  of  Parkman's  Lily,  which  is  here  described  nearly  in  full :  — 

"  My  first  attempt  was  to  combine  the  two  superb  Japanese  lilies,  L.  specio- 
sum  (lancifolium)  and  L.  auratum.  The  former  was  used  as  the  female 
parent.  Four  or  five  varieties  of  it,  varying  from  pure  white  to  deep  red,  were 
brought  forward  in  pots  under  glass.  This  was  necessary,  because  L.  speciosum 
does  not  ripen  its  seed  in  the  open  air  in  the  climate  of  New  England.  When 
the  flowers  were  on  the  point  of  opening,  the  anthers  were  carefully  removed 
from  the  expanding  buds  by  means  of  forceps.  As  the  pollen  was  entirely 
unripe,  and  as  pains  were  taken  to  leave  not  a  single  anther  in  any  of  the 
flowers,  self-impregnation  was  impossible.  The  pollen  of  L.  auratum  was 
then  applied  to  the  pistils  as  soon  as  they  were  in  condition  to  receive  it. 
Impregnation  took  place  in  most  cases.  The  seed-pods  swelled,  and  promised 
an  ample  crop  of  seed;  but  the  experiment  was  spoiled  by  the  bad  management 
of  the  man  in  charge  of  the  greenhouse,  in  consequence  of  which  the  pods  were 
attacked  by  mildew. 

"  In  the  next  year  I  repeated  the  attempt,  with  the  same  precautions. 
This  time  the  seed  was  successfully  ripened.  Being  sown  immediately,  a  por- 
tion of  it  germinated  in  the  following  spring,  and  the  rest  a  year  later.  In 
regard  to  this  seed ,  two  points  were  noticeable :  first,  it  was  scanty,  the  pods 
(though  looking  well)  being  in  great  part  filled  with  abortive  seed,  or  mere 
chaff ;  and,  next,  such  good  seed  as  there  was  differed  in  appearance  from  the 
seed  of  the  same  lily  fertilized  by  the  pollen  of  its  own  species.  The  latter  is 
smooth,  whereas  the  hybrid  seed  was  rough  and  wrinkled.  About  fifty  young 
seedlings  resulted  from  it;  and  their  appearance  was  very  encouraging,  because 
the  stems  of  nearly  all  were  mottled  in  a  manner  characteristic  of  L.  auratum, 
but  not  of  L.  speciosum.  Here,  then,  was  a  plain  indication  of  the  influence 
of  the  male  parent.  The  infant  bulbs  were  pricked  out  into  a  cold-frame,  and 
left  there  three  or  four  years,  when,  having  reached  the  size  of  a  pigeon's  egg, 
they  were  planted  in  a  bed  for  blooming.  This  was  in  1869.  Towards  mid- 
summer, one  of  the  young  hybrids  showed  a  large  flower-bud  much  like  that 
of  its  male  parent,  L.  auratum.  The  rest,  about  fifty  in  all,  showed  no  buds 
until  some  time  after  ;  and  when  the  buds  at  length  appeared,  they  were  pre- 
cisely like  those  of  the  female  parent,  L.  speciosum.  The  first  bud  opened  on 
the  7th  of  August,  and  proved  a  magnificent  flower,  nine  and  a  half  inches  in 
diameter,  resembling  L.  auratum  in  fragrance  and  form,  and  the  most  bril- 
liant varieties  of  L.  speciosum  in  color.  In  the  following  year  it  measured 
nearly  twelve  inches  from  tip  to  tip  of  the  extended  petals  ;  and  in  England  it 
has  since  reached  fourteen  inches.  ...  In  this  one  instance  the  experiment 
had  been  a  great  success;  but  of  the  remaining  fifty  hybrids,  not  one  produced 
a  flower  in  the  least  distinguishable  from  that  of  the  pure  L.  speciosum.  Th« 


458  REPRODUCTION. 

1182.  Focke  has  shown  that  hybrids  between  remotely  related 
species  are  generally  delicate  and  difficult  of  cultivation,  but  that 
those  which  result  from  nearly  related  species  are  remarkable  for 
the  vigor  of  their  vegetative  organs.     Nageli  has  also  pointed 
out  that  the  latter  have  a  somewhat  longer  lease  of  life  than  the 
parents  ;  thus  annuals  can  become  biennials  or  even  perennials. 

1183.  Hybrids  between  closely  related  species  usually  have 
larger  or  more  showy  flowers  than  either  of  the  parents,  but  their 
reproductive  organs  are  much  weaker.     This  diminution  of  fer- 
tility may  be  complete,  but  it  is  usually  only  partial.     The  pollen- 
grains  are  generally  fewer  and  often  less  developed,  the  ovules 
are  less  likely  to  afford  sound  germs.     As  a  rule,  the  stamens 
are  more  affected  than  the  pistils. 

1184.  Derivative  hybrids  are  the  offspring  resulting  from  a 
union  of  a  hybrid  with  one  of  the  parent  forms,  or  with  another 
hybrid  from  a  different  source.     In  the  former  case  there  is  fre- 
quently observed  a  marked  tendency  towards  reversion,  which 
may  be  heightened  by  repeated  experiments  in  the  same  direc- 
tion, until  at  last  it  is  complete. l 

1185.  Hybrids  and  their  offspring  exhibit  a  marked  tendency 
to  vary.    This  fact  is  utilized  by  horticulturists  in  the  production 
of  new  varieties.     Varieties  thus  produced  must,  however,  be 
perpetuated  by  other  means  than  by  seed.8 

influence  of  the  alien  pollen  was  shown,  as  before  noticed,  in  the  markings  of 
the  stem,  and  also  in  a  diminished  power  of  seed-bearing  ;  but  this  was  all. 

"  In  the  next  year,  wishing  to  see  if  the  male  parent  would  not  make  his 
influence  appear  more  distinctly  in  the  second  generation,  I  fertilized  several 
of  these  fifty  hybrids  with  the  pollen  of  L.  auratum,  precisely  as  their  fe- 
male parent  had  been  fertilized.  The  crop  of  seed  was  extremely  scanty  ;  but 
there  was  enough  to  produce  eight  or  ten  young  bulbs.  Of  these,  when 
they  bloomed,  one  bore  a  flower  combining  the  features  of  both  parents  ; 
but,  though  large,  it  was  far  inferior  to  L.  Parkmanni  in  form  and  color. 
The  remaining  flowers  were  not  distinguishable  from  those  of  the  pure 
L.  speciosum"  (Bulletin  of  the  Bussey  Institution,  ii.,  1878,  p.  161). 

1  For  a  full  treatment  of  this  subject,  the  student  should  examine  Nageli's 
treatise  in  Sitzungsberichte  der  Kbnigl.-bayer.-Akad.  der  Wissenschaften  zu 
Miinchen,  1865,  ii.  ;  and  that  by  Focke,  Pflanzen-misclUinge,  1881. 

2  For  a  full  account  of  the  variation  of  hybrids,  the  student  should  see 
Naudin,  Ann.  des  Sc.  nat.,  ser.  4,  1863,  tome  xix. 

For  a  study  of  the  influence  of  foreign  pollen  on  the  form  of  .the  fruit,  see 
a  paper  by  Maximowicz  :  St.  Petersb.  Acad.  Sci.  Bull,  xvii.,  1872,  col.  275. 


CHAPTER  XV. 

THE  SEED    AND   ITS    GERMINATION. 

1186.  THUS  far  this  treatise  has  dealt  chiefly  with  the  phenom- 
ena presented  by  the  organs  of  adult  plants,  especially  while 
these  are  in  a  healthy  state.     It  is  necessary  to  consider  in  con- 
clusion a  special  case  ;  namely,  that  of  the  seed,  and  the  earliest 
phases  of  its  independent  existence. 

1187.  When  a  fertilized  ovule  approaches  maturity,  its  activi- 
ties become  notably  lessened  in  degree  until,  with  perfect  ripe- 
ness of  the  seed,  the  embryo  manifests  no  indication  of  life.     In 
a  few  cases  the  seed  is  so  precocious  that  it  will  germinate  even 
before  it  is  detached  from  the  parent  plant ;  but  there  is  usually 
a  period  of  suspended  activity. 

1188.  Two  views  are  held  as  to  the  nature  of  the  life  of  the 
embryo  during  this  period  of  arrested  activity:  (1)  that  it  is 
simply  potential,  and  may  be  roughly  compared  to  the  fire  in  a 
match,  ready  to  manifest  itself  under  favorable  conditions ;  (2) 
that  it  is  a  sluggish,  dormant  state,  which  differs  from  active  life 
only  in  degree. 

1189.  From  the  first  point  of  view  it  is  easy  to  regard  the 
seed  as  representing  a  certain  amount  of  potential  energy  indi- 
rectly derived  from  solar  radiance,  and  held  for  a  time  in  a  con- 
dition from  which  it  may  be  released  in  many  wa}-s  :  thus,  it  may 
be  liberated  by  rapid  combustion,  as  when  corn  is  burned  for 
fuel ;  by  slow  oxidation,  as  when  seeds  decay  ;  or  by  the  act  of 
germination. 

1190.  The  second  view  takes  into  account,  although  it  does 
not  explain,  the  slight  changes  which  take  place  in  certain  seeds 
and  some  other  parts,  especially  buds,  during  what  has  been 
called  the  resting  state. 

1191.  It  has  been  stated  (976)  that  many  seeds  cannot  be 
made  to  start  into  active  growth,  even  under  the  most  favorable 
external  conditions,  until  after  the  lapse  of  a  definite  period. 
Nothing  is  yet  known  as  to  the  exact  structural  and  other  changes 
which  go  on  by  virtue  of  this  peculiarity. 


460  THE  SEED   AND   ITS  GERMINATION. 

1192.  Ripening  of  fruits  and  seeds.     The  structural  changes 
attending  this  process,  taken  together,  result  in  adaptations  for 
providing  the  embrj'O  with  an  ample  supply  of  food,  for  giving  it 
adequate  protection  during  its  resting  state,  and  for  securing 
its  dissemination. 

1193.  The  chemical  changes  comprise  chiefly  the  storing  up 
of  a  sufficiency  of  food  of  a  proper  character  to  support  the 
embryo  for  a  time.     In  pulpy  fruits  they  are  mostly  associated 
with  the  consumption  of  a  certain  amount  of  oxygen  and  the 
liberation  of  more  or  less  carbonic  acid.     Many  of  the  chemical 
changes  can  go  on  after  the  separation  of  the  fruit  or  seed  from 
the  parent  plant. 

In  the  ripening  of  pulpy  fruits  the  important  changes  in 
texture  are  attended  by  the  formation  of  sugars,  acids,  etc.,  and 
b}-  modifications  in  the  character  of  the  walls  of  cells. 

1194.  Dissemination  is  most  frequently  secured  by  (1)  some 
mechanism  for  transport  by  air,  water,  fleece,  or  plumage ;  (2) 
the  construction  of  some  expulsive  apparatus ;  (3)  the  existence 
of  certain  attractions  of  taste,  color,   and  odor,   by  which  the 
seeds  are  made  the  food  of  birds.     In  the  last  case  the  germ 
itself,  protected  against  the  action  of  digestive  juices,  is  often 
carried  to  great  distances  from  the  parent  plant. 

1195.  Ripeness  of  seeds.     The  embryo  is  sometimes  viable,  or 
capable  of  independent  life,  at  a  very  early  stage.     Immature 
seeds  are  of  course  deficient  in  their  supply  of  proper  food  for 
the  embryo,  which  is  only  imperfectly  developed,  and  their  in- 
teguments are  not  yet  adapted  to  protect  the  germ  adequately. 
But  in  certain  instances  such  seeds  may  germinate,  giving  rise 
to  strong  and  healthy  plants.    Cohn  l  has  shown  that  seeds  which 
are  not  perfectly  ripe  germinate  somewhat  sooner  than  those 
which  are  more  mature  ;  this  means  that  the  store  of  food  is  in 
a  condition  which  admits  of  immediate  use.     He  has  further 
pointed  out  that  seeds  separated  from  the  plant,  but  still  enclosed 
in  the  pericarp,  ripen ;  and  he  believes  that  those  seeds  which 
have  reached  a  medium  stage  of  ripeness  germinate  most  readily. 
"  Viability  does  not  coincide  with  ripeness  ;  it  precedes  it" a 

1196.  Shortly  before  the  period  of  ripening,  the  part  which 

»  Flora,  1849,  p.  481. 

2  There  is  some  reason  to  believe  that  in  the  case  of  certain  cultivated  vege- 
tables unripe  seeds  may  give  rise  to  earlier  varieties  than  come  from  ripe  seeds. 
For  numerous  citations  from  the  extensive  literature  of  the  subject  see  a  paper 
by  the  author  in  the  Report  of  the  Secretary  of  the  Massachusetts  Board  of 
Agriculture  for  1878. 


VITALITY  OF  SEEDS. 


461 


connects  the  fruit  or  seed  with  the  parent  plant  undergoes  marked 
changes,  which  ultimately  effect  or  permit  complete  separation 
of  the  seed  from  the  plant  without  any  injury.  The  process  of 
separation  has  been  compared  to  that  by  which  the  leaf  is  de- 
tached from  the  branch  in  the  autumn. 

1197.  How  long  can  a  seed  retain  its  yitality?  Some  seeds 
perish  shortly  after  separation  from  the  parent  unless  they  are 
at  once  planted,  while  others  preserve  their  vitality  for  long 
periods.  In  experiments  by  De  Candolle  seeds  of  three  hun- 
dred and  sixty-eight  species  of  plants  were  kept  in  the  same 
place  and  under  the  same  conditions  for  fifteen  years.  The 
following  results  are  recorded:  — 

1  came  up,  or  100  per  cent. 


Of    1  Balsaminaceae 


"  50 
"  20 
"  Si 


lOMalvaceje 5 

45  Leguminosse 9 

30  Labiate 1 

10  Scrophulariacese 0 

10  Umbellifene 0 

16  Caryophyllaceae 0 

32  Gramineae 0 

34  Cruciferae 0 

45  Composite 0 


1198.  Daubeny,  Henslow,  and  Lindley  found  that  the  seeds 
of  a  species  of  Colutea  germinated  when  forty-three  years  old,  and 
those  of  a  Coronilla  when  forty-two  years  old.  They  ascertained 
that  the  seeds  of  plants  belonging  to  twent}7  genera  experimented 
on,  germinated  after  from  twenty  to  twenty-nine  years'  separa- 
tion from  the  parent  plant.1 

There  is  no  unquestioned  evidence  that  wheat-grains  from  the 
wrappings  of  mummies  have  been  made  to  germinate.2 


1  Report  of  the  British  Association  for  the  Advancement  of  Science,  1850, 
p.  165. 

2  The  following  notes  of  cases  of  prolonged  vitality  may  be  of  interest :  — 
M.  R.  Brown  ra'a  dit  avoir  fait  germer  des  graines  de  Nelumbium  specio- 

sum  extraites  par  lui  de  1'herbier  de  Sloane,  c'est-a-dire  ayant  au  moins  150 
ans  (De  Candolle:  Geographic  Botanique  raisonnee,  1855,  p.  542). 

Seeds  of  Nelumbium  (jaune)  have  sprouted  after  they  had  been  in  the  ground 
for  a  century  (Lyell's  Second  Visit  to  the  United  States,  ii.,  1849,  p.  ?28). 

The  grains  of  wheat  found  in  mummy-wrappings  are  uniformly  blackened 
as  if  by  slow  charring  (eremacausis),  and  there  is  no  evidence  of  a  trustworthy 
character  that  such  seeds  have  ever  been  made  to  germinate.  The  account 
by  Count  von  Steinberg  of  the  germination  of  wheat  supposed  to  have  been 
procured  at  the  unrolling  of  a  mummy  will  be  found  in  Isis,  1836,  col. 
715-717. 


462 


THE   SEED   AND   ITS  GERMINATION. 


GERMINATION. 

1199.  Germination,1  the  process  by  which  an  embryo  unfolds 
its  parts,  is  complete  when  the  plantlet  can  lead  an  independent 
existence. 

1200.  The  conditions  necessary  for  germination  are  (1)  moist- 
ure, (2)  free  oxygen,  (3)  warmth. 

1201.  The  amount  of  water  required  to  initiate  the  process 
of  germination  is,  in  general,  that  which  will  completely  saturate 
and  soften  the  seed.     Germination  does,  however,  begin  in  cer- 
tain cases  even  when  only  the  radicle  and  the  albumen  directly 
around  it  have  become  soaked. 

The  amount  of  water  requisite  for  the  saturation  of  a  seed  has 
been  determined  for  a  large  number  of  plants,  and  will  be  seen 
by  a  comparison  of  the  results  to  vary  within  wide  limits,  depend- 
ing on  the  percentage  of  water  already  present  and  the  character 
of  the  albumen.  It  is  plain  that  in  very  exact  determinations 
account  must  be  taken  of  the  possibility  of  a  loss  by  the  seed 
of  a  portion  of  its  contents  while  in  water ;  in  three  days  this 
amounts  in  the  common  bean  to  a  little  over  two  per  cent.  The 
cereals  require  a  comparativel}'  small  amount  of  water  for  satu- 
ration, while  leguminous  seeds  absorb  a  much  larger  quantity.2 

1  It  is  well  to  distinguish  between  two  stages  in  the  process  of  germination, 
(1)  that  marked  by  the  protrusion  of  the  first  rootlet,  (2)  the  subsequent  de- 
velopment of  the  embryo  into  an  independent  plant.     The  reason  for  making 
this  distinction  is,  that  most  of  the  experiments  upon  the  relations  of  tempera- 
ture, etc.,  to  germination  have  usually  terminated  at  the  first  stage  ;  whereas 
the  vigor  of  the  plantlet  as  seen  at  a  later  stage  is  an  important  factor  in 
deducing  results  to  guide  practice  in  sowing  seeds. 

2  The  table  below,  by  Hoffmann  (Vereuchs-Stationen,  vii.,  1865,  p.  52),  has  a 
parallel  column  of  results  obtained  at  Tharandt  (Nobbe:  Samenkunde,  p.  119): 


Species. 

Percentage  of  liquid  water  absorbed. 

Observations  by 
Hoffmann. 

Observations  at 
Tharandt. 

44. 
45.5 
46.9 
67.7 
59.8 
92.1 
101 

1068 

117.5 
120.5 
126.7 

39.8 
60. 

157. 
(a.  96. 
1  b.  71. 
105.3 

89. 

Wheat                                           . 

Buckwheat  ... 
Rye  
Oats 

White  beans     .    .            ... 

Windsor  bean  

Peas    

Red  clover    .             

Siisrarbeet  
White  clover 

ABSORPTION    OF   WATER   BY   SEEDS. 


463 


1202.  The  increase  of  seeds  in  size  accompanying  the  absorp- 
tion of  water  is  ascertained  by  placing  them  from  time  to  time 
in   a   narrow  graduated   cylinder,  pouring  over  enough  water 
to  completely  cover  them,  and  noting  the  height  at  which  the 
water  stands  ;  then  pouring  it  into  another  graduated  glass  and 
accurately  measuring  it.     The  difference  in  amount  of  water  in 
each  case  indicates  the  volume  of  the  seeds.     The  work  must 
be  done  expeditiously  in  order  to  avoid  the  error  arising  from 
absorption  during  the  period  of  measuring ;    but  this  error  in 
any  case  is  slight. 

1203.  The  following  results  may  be  of  interest  and  serve  as  a 
guide  to  the  student.1 

65.418  grams  of  air-dried  peas,  having  a  volume  of  43  cubic 
centimetres,  were  soaked  in  water  at  a  temperature  of  19°- 
21°  C.  The  soaked  seeds  were  at  each  measurement  carefully 
dried  by  blotting-paper :  — 


Time. 

1.  In  absolute  figures. 

2.  In  percentages. 

Weight. 

Volume 

Weight. 

Volume. 

14  hours  .  .  . 
41  "  ... 
70  "  ... 

46.41  gr. 
8.02    " 
8.52    " 

46  cc. 
19    " 
7    " 

70.9 
12.3 
13 

107 
44.1 
16.3 

70  hours  .  .  . 

62.95  gr. 

72  cc. 

96.2 

167.4 

The  gain  in  weight  in  70  hours  was  therefore  96  per  cent,  and 
in  volume  167  per  cent. 

In  another  experiment  the  changes  were  as  follows  :  Phaseolus 
vulgaris  gained  in  weight,  in  48  hours,  100.7  per  cent,  and  in 
volume,  134.14  per  cent.  In  still  another  experiment,  with  the 
same  species,  the  gain  in  weight  in  72  hours  was  114.5  per  cent 
(or,  taking  into  account  some  loss  by  extraction,  117.5  per  cent), 
and  in  volume,  140.9  per  cent.  The  gain  in  volume  is  con- 
siderably greater  than  the  gain  in  weight.2 

1  Nobbe  :  Handbuch  der  Samenkunde,  1876,  p.  122. 

2  It  must  be  noted  that  in  many  dry  seeds,  for  instance  between  the  coty- 
ledons of  some  peas  and  beans,  there  are  cavities  which  must  be  filled  before 
there  can  be  any  marked  increase  of  volume  (Nobbe  :   Handbuch  der  Samen- 
kunde, 1876,  p.  125). 


464 


THE   SEED   AND   ITS   GERMINATION. 


1204.  The  greater  part  of  the  increase  in  weight  and  volume 
from  the  absorption  of  water  by  dry  seeds  takes  place  in  a  short 
time  ;  for  example  :  — 


Phaseolus  vulgaris. 

Increase  in 
weight. 

Increase  In 
volume. 

In    6  hours    
«'    9     "             .          

13.99  per  cent. 
18.63  "     " 

28.  28  per  cent. 
13.10   "     " 

"  23     " 

49  42  "     " 

62  07    "     " 

"  28     "  

3.35  "     " 

3.45    "     " 

After  this  there  was  very  little  gain  either  in  weight  or  volume. 

1205.  Access  of  free   oxygen   must  be  provided  to  secure 
germination.     Even  if  all  other  conditions  are  favorable,  germi- 
nation does  not  take  place  in  pure  water  devoid  of  any  free 
oxygen,  or  in  an  atmosphere  of  nitrogen. 

1206.  The  oxygen  accessible  to  the  seed  must  be  diluted  to 
about  the  degree  found  in  common  atmospheric  air,  although  it 
is  not  necessary  that  the  dilution  should  be  made  with  nitrogen, 
as  is  the  case  with  air.     Boehm 1  has  shown  that  a  mixture  of 
proper  proportions  of  hydrogen  and  oxygen  answers  about  as 
well  as  a  mixture  of  nitrogen  and  oxygen  for  germination  of 
seeds,  provided  it  is  furnished  to  them  under  ordinary  atmos- 
pheric pressure.     That  the  degree  of  pressure  is  an  important 
factor,  is  proved  by  Bert's 2  experiments.      Barley  gave  the 
following  results :  — 

Percentage  germinated. 

In  ordinary  air  (76  cm.  pressure) 84 

In  air  50    "        "         40 

"    "  25   "         "          28 

6    "         "         10 

The  proportion  of  oxygen  to  nitrogen  in  atmospheric  air  is 
approximately  1  :  5  (oxygen,  21,  nitrogen,  79  parts). 

1207.  The  temperature  requisite  for  germination  to  begin 
differs  considerably  in  different  species.     The  lowest  tempera- 
ture recorded  is  the  following,  noted  by  Uloth : 8  In  a  perfectly 
dark  ice-cellar  seeds  of  Acer  platanoides  sprouted  on  ice,  the 
rootlets  penetrating  to  a  depth  of  5  to  7.5  cm.  into  the  dense 

1  Sitzber.  :  Wien  Akad.,  bcviii.,  1873,  p.  132. 
a  Comptes  Rendus,  Ixxvi.,  1875,  p.  1493. 
»  Flora,  1871,  p.  185. 


TEMPERATURE   REQUISITE   FOR   GERMINATION.      465 

clear  ice  ;  the  seeds  themselves  being  in  hollows  on  its  surface. 
The  temperature  must  of  course  be  given  as  0°  C.  Uloth  found 
also  that  wheat-grains  germinated  in  the  same  cellar  upon  pieces 
of  ice.  Kerner 1  placed  seeds  with  some  earth  in  glass  tubes  and 
exposed  them  to  the  cold  springs  on  the  edge  of  snow-fields  in 
Alpine  regions.  He  found  that  the  seeds  of  most  Alpine  plants 
could  germinate  at  2°  C.,  and  that  some  might  even  at  0°.  It 
was  shown  that  at  all  growing  points  there  is  some  heat  evolved. 
In  Uloth's  observatioas,  above  noted,  attention  is  called  to  the 
fact  that  the  rootlets  descended  into  solid  ice  in  a,  number  of 
cylindrical  cavities  which  they  melted  out  for  themselves. 

1208.  The  minimum  temperature  for  germination  of  the  seeds 
of  many  plants  in  common  cultivation  is  given  by  Haberlandt 2 
as  4°. 75  C.  (although  some  can  start  even  below  this).      Be- 
tween 4°. 75  and  10°.5  we  have  the  minimum  temperature  for 
Indian  corn,  ti moth y  grass,  sunflower;  between  10°. 5  and  15°. 6, 
that  for  tobacco  and  squash  ;  between  15°.6  and  18°.5,  that  for 
cucumber  and  melon. 

1 209.  The  maximum  temperature,  or  that  beyond  which  germi- 
nation cannot  begin,  differs  greatly  in  different  species.     Haber- 
landt has  shown  that  degree  of  ripeness,  freshness,  the  "  race," 
and   several   other  influences   considerably  modify   the   result. 
The  maximum  temperature  for  a  few  of  the  more  common  plants 
is  here  noted :  — 

c°. 
Wheat,  rye,  barley,  oats,  peas,  timothy  grass,  cabbage,  poppy,  flax, 

and  tobacco 31-37 

Red  clover,  lucerne,  buckwheat,  and  sunflower 37.5-44 

Indian  corn,  millet,  squash,  cucumber,  and  sugar  melon      ....      44-50 

In  no  case  was  germination  observed  above  50°  C. 

1210.  Between  the  minimum  temperature  below  which  and 
the  maximum  temperature  above  which  germination  of  a  cer- 
tain kind  of  plant  does  not  ordinarily  take  place  there  lies  an 
optimum  temperature ;  that  is,  the  degree  at  which  germina- 
tion begins  most  speedily.8    The  short  table  on  the  following 
page  is  by  Sachs :  — 


1  Berichte  der  naturw-med.  Vereines  in  Innsbruck,  1873,  and  Botanische 
Zeitung,  1873,  p.  437. 

2  Versuchs-Stationen,  xvii.  p.  104. 

8  The  difference  in  regard  to  the  degree  of  warmth  demanded  by  seeds  of 
the  same  species  raised  in  different  climates  has  been  examined  by  Schiibeler 
(Die  Culturpflanzen  Norwegens,  1862,  p.  27). 
30 


466 


THE    SEED    AND    ITS    GERMINATION. 


Minimum. 

Maximum. 

Optimum. 

Barley   

5° 

38° 

29° 

Wheat   '  . 

5° 

42° 

29° 

Scarlet  runner      .     .     . 

9.°5 

46° 

33° 

Indian  corn     .     .     .    . 

9.°5 

46° 

33° 

Squash  

11° 

46° 

33° 

1211.  The  time  required  after  planting  for  germination  to 
begin,  a  point  indicated  by  the  protrusion  of  the  radicle,  has 
been  determined  1  for  a  large  number  of  plants.  A  few  exam- 
ples are  here  mentioned :  — 


Indian  corn. 

Bed  clover. 

Birch. 

Atl6°C  
"  25°  C.  .  ... 

144  hours. 
56      " 

32  hours. 
24      " 

120  hours. 
24      " 

"  31°  C  
"  37°  5  C  

48      " 
48      " 

24      " 

24      " 

24      " 
24      " 

"  44°  C  

80      " 

72      " 

1212.  The  influence  of  light  upon  the  earliest  stages  of  germi- 
nation has  been  shown  by  careful  investigations  to  be  inappre- 
ciable so  far  as  most  plants  are  concerned.2 

The  unqualified  statement  found  in  some  works,8  that  light  is 
in  general  prejudicial  to  germination,  is  not  borne  out  by  facts. 

1213.  The  phenomena  of  germination  are  :  (1)  forcible  absorp- 
tion of  water,  (2)  absorption  of  oxygen,  (3)  solution  of  nutrient 
matters,  (4)  their  transfer  to  points  of  consumption,  (5)  their 
employment  in  building  up  new  parts.     After  the  initial  step 
these  processes  may  go  on  simultaneously. 

1214.  The  enormous  imbibition  power  of  dry  seeds  can  be 
demonstrated  by  confining  sound  seeds  in  a  strong  receptacle 
to  which  water  can  obtain  access.     If  a  closed  manometer  is 
attached,  the  pressure  they  exert  can  be  measured.     Boehm  4 

1  Versuchs-Stationen,  xvii.,  1874,  p.  104  ;  and  Storer  :  Bulletin  Bussey 
Inst.,  1884. 

a  Hoffmann  :  Jahresber.,  iiber  Agricultur-Chem.,  1864,  p.  110. 

8  Ingenhousz  ;  Senebier,  Physiologic  vege"tale,  iii.  1800,  p.  396  ;  Johnston's 
Lectures  on  Agricultural  Chemistry,  1842,  p.  194. 

4  Miiller:  Botan.  Unters.  ii.,  1872,  p.  29,  quoted  by  Nobbe  (Hand- 
buch  der  Samenkunde,  p.  118).  Similar  experiments  at  Wellesley  College 
gave  results  somewhat  lower  than  this. 


PHENOMENA   OF   GERMINATION.  467 

found  that  peas  in  swelling  could  overcome  a  pressure  of  18 
atmospheres,  corresponding  to  a  height  of  the  mercurial  column 
of  13.5  metres. 

1215.  The  influence  of  oxygen  upon  the  absorption  of  water 
by  the  seed  is  not  marked,  as  will  be  seen  by  the  following 
experiment : a  — 

200  fresh  seeds  of  red  clover  were  placed  in  pure  water  for  20 
hours ;  200  more  were  placed  in  water  into  which  oxygen  gas 
was  conducted ;  200  more  in  water  through  which  carbonic  acid 
gas  was  conducted  for  a  while  and  then  the  water  covered  with 
a  layer  of  oil  to  exclude  the  air.  The  results,  so  far  as  swelling 
is  concerned,  were  as  follows  :  — 

Seeds  in  water 83  per  cent  swollen. 

"      with  oxygen  ....     86       "  " 

"         "    carbonic  acid  .     .     71       "  " 

1216.  The   oxygen    absorbed  by  seeds  in    germination   was 
thought  by  Schonbein  to  undergo  the  active  or  ozone  modifica- 
tion.   By  his  experiments  the  seeds  of  two  plants,  Cynara  Scoly- 
mus  and  Scorzonera  Hispanica,  were  shown  to  possess  to  a  con- 
siderable degree  the  power  of  converting  atmospheric  oxygen 
into  ozone. 

1217.  Oily  seeds  absorb  a  large  amount  of  oxygen.     Siewert 
has  pointed  out  the  fact  that  the  neutral  oil  of  the  rape-seed  very 
soon  after  access  of  oxygen  and  water  to  it  possesses  an  acid 
reaction.     Oleic  acid  can  absorb  at  ordinary  temperatures  about 
twenty  times  its  volume  of  oxygen. 

1 218.  Nutrient  matters  must  become  liquid  before  they  can  be 
utilized  by  the  embryo.     Some  of  these  in   the  form  in  which 
they  are  stored  up  in  seeds  are  soluble  in  water ;  such  are  the 
sugars,  dextrin,  and  a  part  of  the  albumin.     The  other  nutrient 
matters,  such  as  starch,   the  oils,  and   most  nitrogenous  sub- 
stances, must  undergo  changes  before  they  can  enter  into  solu- 
tion.    Some  of  these  changes  have  already  been  alluded  to  in 
Chapter  XI.,  and  are  here  presented  in  brief  review. 

1219.  The  conversion  of  starch  into  soluble  matters  is  effected 
in  the  seed  by  means  of  one  or  more  "  ferments."     In  the  pro- 
cess of  malting,2  which  consists  essentially  in  forcing  germination 
up  to  the  point  of  protrusion  of  the  radicle  and  then  checking  it, 
the  starch  appears  to  undergo  little  change.     But  if  the  ground 
malted  grains  are  kept  in  water  of  a  temperature  of  68°  C.  for 

1  Nobbe  :  Handbuch  der  Samenkunde,  1876,  pp.  102,^103. 

2  See  Watts's  Dictionary  of  Chemistry,  under  "  Beer." 


468  THE   SEED   AND    ITS   GERMINATION. 

two  hours,  all  the  starch  will  be  found  to  have  been  converted 
into  and  dissolved  as  soluble  carbohydrates,  sugar,  and  dextrin. 
The  change  in  this  case  is  attributed  to  the  ferment,  diastase, 
one  part  of  which,  it  is  claimed,  can  convert  two  thousand 
parts  of  starch  into  sugar.  It  will  be  noted  that  in  the  pro- 
cess above  described  the  temperature  (68°  C.)  is  much  higher 
than  that  at  which  ordinary  germination  proceeds. 

Dubrunfaut 1  has  given  the  name  maltin  to  a  ferment  far  more 
active  than  diastase,  found  in  ah1  germinating  cereals.  This  is 
able  to  convert  into  a  soluble  state  from  one  hundred  thousand 
to  two  hundred  thousand  times  its  weight  of  starch.  It  forms 
with  tannic  acid  an  insoluble  compound  which  retains  its  power 
for  a  long  time.  In  good  barley  meal  there  is  one  per  cent  of 
maltin. 

1220.  The  oil  in  oily  seeds  is  in  germination  carried  through 
a  long  series  of  changes.     It  is  first  transformed  into  starch,  and 
then  follows  the  same  course  as  starch,  alread}'  described.2 

1221.  Van  Tieghein  has  shown  that  oleaginous  albumen,  rich 
in  aleuron,  has  an  activity  of  its  own  which  enables  it  to  digest 
itself,  so  to  speak,  and  thus  become  at  once  fit  for  the  embryo 
to  use ;  on  the  other  hand  starchy  albumen  and  cellulosic  albu- 
men must  be  first  acted  on  by  the  embryo,  and   thus  become 
dissolved  and  ready  for  use.8 

1222.  The  changes  which  take  place  in  a  germinating  seed 
are  accompanied  by  direct  or  indirect  oxidation  of  a  portion  of 
the  nutrient  matters,  a  release  of  energy,  and  an  evolution  of 
carbonic  acid.4    The  amount  of  CO2  given  off  by  germinating 
seeds  and  the  rise  of  temperature   serve  as  measures   of  the 
process  of  oxidation. 

1223.  It  is  not  proved  that  germination  can  be  hastened  by 
chemical  means.     Experiments  with  dilute  chlorine  water  seem 
to  show  that  the  time  can  be  somewhat  lessened,  but  the  results 
are  discordant.6 

1224.  It  has  been  asserted  recently  that  the  presence  of  mi- 
crobes, the  minute  organisms  to  which  putrefaction  is  due,  is 

1  Comptes  Rendus,  Ixvi.,  p.  274. 

a  Peters,  Vereuchs-Stationen,  iii.,  1861,  p.  1  ;  Miintz,  Ann.  de  Chimie  et 
de  Physique,  ser.  4,  tome  xxii.  p.  472. 

8  Ann.  des  Sc.  iiat.,  ser.  6,  tome  iv.,  1877,  p.  189. 

*  For  the  changes  in  the  horny  endosperm  of  the  date  palm  see  Sachs, 
Botanische  Zeitung,  1862,  p.  241. 

6  See  M.  Carey  Lea,  American  Journal  of  Science,  xxvii.,  1864,  p.  373, 
and  xliii.,  1867,  p.  197. 


FIRE-WEEDS.  469 

essential  to  the  beginning  of  the  process  of  germination.  It  is 
said  that  in  soil  which  has  been  completely  sterilized,  that  is, 
freed  from  microbes  or  their  germs,  seeds  provided  with  all  other 
requisites  for  germination  will  fail  to  sprout.  These  experiments 
by  Duclaux  1  have  not  been  repeated  by  other  observers. 

1225.  The  appearance  of  abundant  crops  of  certain  plants 
upon  ground  recently  cleared  by  fire  is  one  of  the  most  note- 
worthy phenomena  in  connection  with  germination.  At  the 
North,  two  plants  have  obtained,  par  excellence,  the  name  of 
11  fire-weeds ;"  namely,  Erechtites  hieracifolia,  and  the  more 
common  willow-herb,  or  Epilobium  angustifolium.  They  are 
later  replaced  by  shrubs,  and  later  still  by  soft- wooded  trees, 
which  are  characteristic  of  burnt  districts.  The  following  sug- 
gestions have  been  made  in  regard  to  their  appearance :  (1)  that 
the  seeds  have  been  long  buried  in  the  soil,  under  conditions 
which  have  preserved  their  vitality,  but  which  did  not  permit 
them  to  germinate ;  (2)  that  the  seeds  find  their  way  to  the 
ground  of  a  clearing  which  affords,  in  the  ash  released  from 
wood  by  burning,  a  soil  most  fit  for  germination.  But  no  exact 
observations  have  yet  been  made  upon  the  subject. 

1  Comptes  Rendus,  c.,  1885,  p.  67. 


CHAPTER  XVI. 

RESISTANCE  OP    PLANTS   TO   UNTOWARD   INFLUENCES. 

1226.  CLAUDE  BERNARD  has  shown  that  life  presents  itself 
under  three  forms :  (1)  latent,  dormant,  or  inactive,  illustrated 
by  the  seed  ;  (2)  variable,  or  oscillating,  exemplified  by  the  plant 
during  periods  of  apparent  rest,  when  its  activities  are  nearly 
suspended,  but  when,  in  fact,  some  chemical  changes  are  going 
on,  though  very  slight  in  degree ;  (3)  active,  or  free,  exhibited 
by  a  plant  in  full  vigor. 

It  has  been  repeatedly  pointed  out  in  previous  chapters  that 
during  their  resting  periods  seeds  and  other  parts  can  be  sub- 
jected to  the  action  of  influences  which  would  destroy  the  life 
of  plants  in  full  activity.1 

1227.  Inquiry  as  to  the  kind  and  amount  of  injury  caused  to 
active  plants  by  hurtful  agents  must  deal  with  the  influence  of 
extremes  of  temperature,  too  intense  light,  improper  food,  poi- 
sons, and  mechanical  agents.    Many  of  these  injurious  influences 
and  their  effects  upon  special  parts  of  the  plant  have  already 
been  alluded  to  in  previous  chapters ;  but  it  is  proper  to  con- 
sider them  now  with  regard  to  the  whole  organism. 

1228.  Effects  of  too  high  temperature  upon  the  plant.     Here, 
as  in  most  other  cases,  there  is  wide  diversity  among  plants, 
depending  upon  their  constitutional  peculiarities  ;  thus,  plants  of 
the  tropics  not  only  demand  higher  temperatures  than  those  of 

1  For  some  account  of  various  recent  views  in  regard  to  the  nature  of  life, 
the  student  is  referred  to  the  following  works  :  Herbert  Spencer,  Principles  of 
Biology,  1870;  Claude  Bernard,  Lecons  sur  les  Phenomenes  dela  Vie  communs 
aux  Animaux  et  aux  Vegetaux,  1879;  and  Nageli's  recent  treatises. 

For  an  interesting  account  of  the  reactions  of  living  matter  to  very  dilute 
solutions  of  certain  substances  which  are  poisonous  when  used  in  greater 
strength,  see  Loew  and  Bokorny.  These  investigators  use  a  dilute  alkaline 
solution  of  argentic  nitrate  in  the  discrimination  between  living  and  dead 
protoplasm  ;  upon  application  of  the  reagent  the  former  turns  black,  the  latter 
remains  uncolored.  The  solution  is  made  by  mixing  1  cc.  of  a  one  per  cent 
solution  of  the  nitrate  in  distilled  water  with  an  equal  amount  of  a  solution 
containing  13  parts  of  potassic  hydrate  solution,  10  parts  of  ammonia,  and 
77  parts  of  distilled  water  (Pfluger's  Archiv.  xxv.,  1881,  p.  150). 


EXTREMES    OF   HEAT   AND   COLD. 


471 


colder  climates  for  the  exercise  of  their  normal  functions,  but 
the}'  will  also  general!}'  sustain  much  higher  degrees  of  heat  with- 
out injury.  The  differences  of  temperature  in  favor  of  tropical 
plants  are  not,  however,  always  very  marked. 

The  following  table l  indicates  sufficiently  the  highest  tempera- 
tures which  a  few  common  plants  can  bear.  The  line  at  the  top 
shows  what  were  the  immediate  surroundings  of  the  plants  ex- 
perimented upon ;  the  columns  marked  A  show  the  highest 
temperatures  short  of  proving  fatal ;  those  marked  B,  the  low- 
est fatal  temperatures.  The  plants  were  exposed  to  the  high 
temperatures  from  fifteen  to  thirty  minutes. 


Name  of  Plant. 

Roots  in  water, 
stems  in  air. 

Roots  in  soil, 
stems  in  air. 

Plant  in  water. 

A. 

B. 

A. 

B. 

A. 

B. 

0  C. 

o 

0 

0 

0 

0 

Zea  Mais 

45.5 

47. 

50.1 

52.2 

46. 

46.8 

Tropseolum  majus 

45.5 

47. 

50.5 

52. 

44.1 

45.8 

Citrus  Aurantium 

47.8 

50.5 

50.3 

52.5 

Phaseolus  vulgaris 

45.5 

47. 

50. 

51.5 

1229.  After  a  plant  has  been  subjected  to  too  high  a  tempera- 
ture, its  foliage  wilts  and  soon  becomes  dry;    and  its  leaves, 
having   once   taken  on  a  scorched   appearance,  are   unable  to 
recover  their  turgescence.     It  may  happen,  however,  that  the 
injury  does  not  proceed  so  far  as  to  affect  the  latent  or  even  the 
partially  developed  buds  ;    if  this  is  the  case,  partial  recovery 
takes  place  through  their  unfolding.      The  curious  fact2  that 
many  algfe  can  resist  very  high  temperatures  has  been  already 
adverted  to  (see  566). 

1230.  Effects  of  cold  upon  the  plant.     Certain  plants  are  seri- 
ously injured  by  low  temperatures  which  are  considerably  above 
the    freezing-point  of  water,  but  these  are  exceptional  cases. 
Most  northern  plants  can  readily  endure  cold,  provided  their 
tissues  are  not  frozen. 

Frost  produces  very  different  effects  upon  different  plants.    1 
some  of  our  familiar  spring  plants  the  leaves  may  be  frozen  and 
thawed  without  apparent  mischief,  but  in  general  the  thawing 
must  take  place  slowly  ;  if  it  proceeds  rapidly,  the  plant  may  b< 


De  Vries:  Archives  Neerlandaises,  v.,  1870. 

Consult  also  American  Journal  of  Science  and  Arts,  xhv.,  1867,  p.  152. 


472  UNTOWABD   INFLUENCES. 

irreparably  injured.    There  are  well-known  cases  in  which  plants 
may  be  thawed  quickly  without  serious  injury.1 

1231.  Goppert2  and  others  have  shown  that  the  flowers  of 
certain  orchids,  turned  blue  by  the  formation  of  indigo  in  their 
cells  when  they  are  slightly  frozen  and  suddenly  thawed,  will 
preserve  their  usual  colors  unchanged  if  made  to  thaw  very 
slowly.8 

1232.  As  to  the  length  of  time  during  which  the  vitality  of  a 
frozen  plant  persists,  we  have  no  exact  observations ;  but  it  is 
stated  that  after  the  recession  of  a  glacier  in  Chamouni  sev- 
eral plants  which  had  been  covered  by  ice  for  at  least  four  years 
resumed  their  growth.4 

1233.  It  is  still  an  open  question  whether  much  of  the  injury 
to  certain  plants  by  freezing  is  not  strictly  mechanical,  resulting 
from  the  expansion  during  the  formation  of  ice  in  the  cells.5 

1234.  "Winterkilling."     The  destruction  of  many  plants  by 
exposure  to  the  influences  of  a  variable  winter  is  sometimes 
attributed  to  the  injurious  effects  of  drying  winds  rather  than 
to  cold  alone.      It  has  been  shown  (748)  that  the  amount  of 
water  absorbed  by  roots  is  governed  largely  by  the  temperature 
of  the  soil.    Although  the  exhalation  of  moisture  from  the  leaves 
of  evergreens  in  winter  is  not  large,  it  is,  however,  sufficient  to 
create  a  certain  demand  upon  the  soil  for  a  supply.     This  de- 
mand, slight  as   it  is,  is  of  course  greater  during  very  dry 
weather ;  and  it  is  from  this  that  the  injuries  may  be  supposed 
largely  to  result. 

1235.  The  behavior  of  certain  plants  during  exposure  to  low 
temperatures  affords  some  of  the  best  illustrations  of  the  adap- 
tation of  vegetation  to  its  surroundings ;    and  the  question  as 
to  increasing  the  tolerance  of  a  given  species  or  variety  to  the 

1  Sachs  has  shown  that  the  leaves  of  cabbage,  turnip,  and  certain  beans 
frozen  at  a  temperature  of  from  —5°  C.  to  —7°  C.,  and  placed  in  water  at  0°  C., 
are  immediately  covered  with  a  crust  of  ice,  upon  the  slow  disappearance  of 
which  they  resume  their  former  turgescence  (Versuchs-Stationen,  ii.  1860,  p. 
167).  If  such  frozen  leaves  are  placed  in  water  of  7.5°  C.  they  become  flaccid 
immediately. 

8  Botauische  Zeitung,  1871,  p.  399. 

8  According  to  Kunisch  (quoted  by  Pfeffer :  Pflanzenphysiologie,  ii.,  p. 
436),  this  blue  discoloration  is  observed  when  the  flowers,  placed  in  an  atmos- 
phere of  carbonic  acid,  are  subjected  to  a  freezing  temperature  :  in  this  case,  of 
course,  the  indigo  is  produced  from  chromogen  without  free  oxygen. 

4  Botanische  Zeitung,  1843,  p.  13. 

6  Hoffmann  (Grundziige  der  Pflanzenklimatologie,  1875,  p.  325)  attributes 
i\  part  of  the  mechanical  injury  from  freezing  to  the  separation  from  the  cell- 
sap  of  the  air  previously  contained  therein. 


IMPROPER   FOOD    AND   POISONS.  473 

untoward  influence  of  cold,  by  careful  selection  of  seed  for  a 
series  of  years,  has  been  successfully  answered  by  cultivators  in 
some  northern  countries  of  Europe.1 

1236.  Among  the  protective  adaptations  of  seedlings  to  cold 
is  that  described  by  De  Vries,2  who  has  noted  that  in  certain 
instances  there  is  a  marked  retraction  of  the  caulicle  into  the 
ground  upon  the  approach  of  a  lower  temperature.     The  with- 
drawal is  due  to  the  contraction  of  the  cellular  tissue  composing 
the  root. 

1237.  Effects  of  too  intense  light  upon  the  plant.      All  other 
conditions  being  natural,  living  plants  containing  chlorophyll  can 
perform  their  functions  normally  when  placed  in  the  brightest 
sunlight.8     Even  when  the  rays  of  light  are  moderately  concen- 
trated upon  the  foliage  by  a  large  convex  lens  there  is  no  seri- 
ous  disturbance  of  function.      But  when,   as   in  Pringsheim's 
experiments  (see  824),  the  sunlight  is  rendered  very  intense, 
assimilation  is  arrested  and  destruction  of  the  protoplasm  soon 
ensues. 

1238.  Effects  of  improper  food  upon  the  plant.     It  has  been 
shown  (Chapters  VIII.  and  X.)  that  certain  substances  are  in- 
dispensable to  the  healthful  growth  of  plants ;  and  it  has  further 
been  pointed  out  that  most  of  these  substances  may  be  offered  to 
the  plant  in  excess  with  no  marked  results.     It  should  now  be 
noted  that  a  few  of  these  substances,  notably  nitrogen  com- 
pounds, applied  in  excess  may  induce  a  more  luxuriant  growth 
than  is  desirable  to  the  cultivator.     Penhallow 4  and  others  have 
pointed  out  that  certain  maladies  of  plants  are  largely  dependent 
upon  malnutrition.     In  such  maladies  fungi  are  frequent  con- 
comitants, in  many  cases  invading  plants  already  enfeebled  by 
improper  or  insufficient  food ;   in  others,  obviously  causing  by 
their  presence  and  activity  the  diseased  conditions. 

1239.  Effects  of  poisons  upon  the  plant.     Noxious  Gases.    The 
most  hurtful  of  these,  considered  from  a  practical  point  of  view, 
come  as  products  of  the  combustion  of  inferior  sorts  of  coal, 

1  Schiibeler  (see  note  on  page  465). 

For  an  account  of  the  formation  of  ice  in  plants,  and  the  different  degrees 
of  temperature  at  which  it  takes  place,  consult  Miiller  :  Landwirthschaftl. 
Jahrhiicher,  ix.,  1880. 

2  Botanische  Zeirung,  1879,  p.  649.     Haberlandt  has  also  examined  the 
same  mechanism  to  some  extent. 

8  It  is  a  familiar  fact  that  many  plants  thrive  best  in  deeply  shaded  glens. 
Success  in  the  cultivation  of  such  plants  is  attained  only  by  regarding  their 
natural  condition. 

*  Houghton  Farm  Experiment  Department,  series  3,  no.  iii. 


474  UNTOWARD   INFLUENCES. 

especially  those  which  contain  sulphur  compounds  as  impurities.1 
Formerly,  in  the  vicinity  of  large  chemical  factories,  the  escaping 
gases  were  productive  of  wide-spread  injury  to  vegetation  ;  but 
improved  methods  of  manufacture  have  diminished  this  evil  to 
a  considerable  extent. 

1240.  Sulphurous  acid,  formed  by  combustion  of  sulphur  in 
the  open  air,  produces,  even  when  existing  in  the  air  in  the  pro- 
portion of  only  one  part  in  9,000,  the  following  effects  upon 
leaves :  their  blades  shrivel  from  the  tips,  become  grayish  yel- 
low, and  soon  dry  so  that  they  fall  off  at  a  slight  touch.     The 
phenomena  observed  are  somewhat  like  those  occurring  at  the 
time  of  the  fall  of  the  leaf  in  autumn.    Yet  in  the  experiments  by 
Turner  and  Christison  mentioned  in  the  note,2  the  amount  of 
sulphurous  gas  present  in  the  air  was  so  small  as  to  escape 
detection  by  smell. 

Hydrochloric  acid  gas,  nitric  acid  in  vapor,  and  chlorine  are 
also  very  destructive  to  plants,  even  when  in  such  minute 
amounts  as  to  be  unnoticed  on  account  of  their  odor. 

Injurious  effects  are  often  produced  upon  shade  trees  by  the 
leakage  of  illuminating  gas  from  street  mains. 

1241.  Wardian  Cases.    In  1829  Ward  accidentally  discovered 
that  plants  could  thrive  in  tightly  closed  cases,  in  which  there 
could  not  be  any  interchange  of  the  air  with  the  outside  atmos- 
phere.8   This  discovery  led  him  to  institute  experiments  rela- 

i  R.  Angus  Smith :  Air  and  Rain,  1872,  pp.  465,  553. 

3  For  accounts  of  experiments  in  this  interesting  field,  the  student  may 
consult  the  following  works  :  Turner  and  Christison,  Edinburgh  Medical  and 
Surgical  Journal,  xxviii.  p.  356;  and  Gladstone  in  Report  of  British  Association 
for  Advancement  of  Science,  1850. 

8  N.  B.  Ward  :  On  the  Growth  of  Plants  in  Closely  Glazed  Cases,  1852. 

The  table  on  the  following  page,  based  on  researches  by  T.  W.  Harris,  shows 
the  agents,  the  effects  of  which  were  tried  upon  chlorophyll,  and  the  results  in 
each  case  as  to  the  extrusion  of  chlorophyll  pigment  (see  772).  The  figures 
in  the  third  column  indicate  results  as  follows:  — 

1.  Chlorophyll  grains  large  and  well  defined.     Sponge-like  structure  evi- 
dent.    One  or  two  globules  of  large  size  on  almost  every  grain  ;  sometimes 
almost  as  large  as  the  grain  itself,  which  is  colorless  or  nearly  so. 

2.  Globules  still  plentiful  but  smaller ;  frequently  several  on  each  grain. 
Structure  of  the  grains  evident.    The  protoplasm  in  this  and  the  two  following 
grades  (3  and  4)  is  often  contracted  by  the  chemicals  used,  rendering  the  result 
more  or  less  obscure. 

3.  Globules  small,  and  fewer  than  in  2.     Grains  still  retain  some  coloring- 
matter  in  their  substance,  and  are  not  so  well  defined  either  in  form  or 
structure. 

4.  Globules  few ;  only  seen  on  a  few  grains.     Structure  of  the  grain  not 
defined,  but  under  a  high  power  it  frequently  has  a  granular  and  sometimes  a 


NOXIOUS   GASES. 


475 


tive  to  the  systematic  cultivation  of  plants  in  such  cases  in  the 
impure  air  of  manufacturing  towns.  In  the  glass  cases,  now 

stellate  appearance.  In  the  latter  case  each  grain  is  generally  surrounded  by 
an  irregular  mass  of  colored  protoplasm,  these  masses  being  often  connected 
together  by  threads.  This  stellate  structure  is  also  often  brought  out  after 
dissolving  out  all  the  coloring-matter  by  prolonged  treatment  with  beuzoic 
acid. 

5.  No  result. 

Agent.  Time  of  Action.  Result. 

(  Grains  bleached,  but  form 
Alcohol  (95%) Iday.j  remains. 

Steam 1  hour.  2 

Boiled  in  H.20 7  min.  2 

then  cold  in  HC1 ... 

-        HN08.         .  , 

«         "         "         "        BenzoicAcid.  2 

U.,S04conc •     •  1    "        Specimen  destroyed. 

KUS04  dilute 1     "  3 

HN08  cone 1    "        Protoplasm  contracted. 

HN08  dilute 1    "  1 

HC1 1    "  2 

(  Protoplasm    much   con- 

HC1  +  HN08  (3  parts  HC1,  1  part  HN03)  1    "     j     tracted. 

H2S04  4-  HC1  (equal  parts) 2  "  3 

H2S04  +  HN08       "  2  " 

HaS04  +  HC1  +  HN08  (equal  parts)  .     .  2  " 

HC2H802 7  ' 

HAO* j  ; 

H8P04 7    *  2 

H2C4H406(TartaricaCid)  {SR^}    7    «  2 

H2Cr04 7  • 

Picric  Acid 7 

Citric  Acid 7  ' 

Boracic  Acid 7  ' 

.   . ,  (  sat.  sol.  in  a  sol.  of  1^  parts  )  ,  ««  l 

Benzoic  Acid  j      N^HpC)4  to  100  H20     J  1 

Benzoic  Acid 2  "       Grains  bleached. 

Salicylic  Acid 3  " 

Na2HP04 6  " 

Na(NH4)HP04 6  " 

NaHS04 6    " 

f  Grains  destroyed  and  pig- 

N  QTT  2    "      -}     ment  diffused  through 

(      the  protoplasm. 

NH4OH 2    " 

K  Of)  2     "  5 

(  Grains  swell  and  become 
1      homogeneous,  but  no 

Ether ^  ^      extrusion  or  escape  of 

'      the  pigment. 


476  UNTOWARD   INFLUENCES. 

everywhere  known  as  Wardian  cases,  the  plants  are  supplied 
with  sufficient  water,  and  the  atmosphere  is  practically  satu- 
rated with  moisture.  When  exposed  to  sunlight,  the  plants  in 
the  cases  can  carry  on  all  the  operations  of  assimilation,  growth, 
and  respiration. 

Comparing  the  conditions  which  surround  the  plants  in  a 
Wardian  case  with  those  which  prevail  in  a  furnace-heated  house, 
it  is  plain  that  the  plants  in  the  case  are  placed  in  what  is  es- 
sentially a  humid  tropical  climate,  while  those  in  the  house 
are  exposed  to  excessive  dryuess,  and  to  an  atmosphere  which 
ma}-  contain  minute  traces  of  the  poisonous  gases  arising  from 
combustion. 

1242.  Liquids  and  Solids.     Comparatively  few  substances 
except  those  possessing  strong  acid  or  alkaline  properties  are 
injurious  to  a  plant.    As  indicated  in  685,  preparations  of  arsenic 
which  are  extensively  employed  for  the  destruction  of  insects 
upon  crops  in  cultivated  fields  are  not  absorbed  by  plants  to  an 
appreciable  extent.     This  is  further  illustrated  by  the  impunity 
with  which  various  other  insecticides  can  be  applied  to  green- 
house plants. 

1243.  Numerous  experiments,  more  curious  than  profitable, 
have  been  made  to  test  the  effect  of  poisonous  alkaloids  upon 
vegetation.      Many   observers   have   proved   that   some    plants 
yielding  poisonous  alkaloids  may  be  poisoned  by  applications 
to  their  roots  of  solutions  of  the  very  alkaloids  which  they  have 
themselves    produced  ;   thus   morphia   may   poison   the   poppy 
(see  961).     Strasburger1  says  that  morphia  speedily  kills  motile 
spores. 

Kiihne2  has  noted  that  the  protoplasmic  movement  in  the 
stamen-hairs  of  Tradescantia  is  not  wholly  arrested,  even  after 
many  hours,  by  a  solution  of  veratrin  ;  and  Pfeffer 8  has  observed 
that  the  cells  in  sections  of  certain  fleshy  roots  are  not  killed 
even  when  immersed  for  several  days  in  a  saturated  solution  of 
morphia  acetate. 

As  Frank 4  suggests,  these  discrepancies  in  effects  depend  on 
the  differences  in  the  power  possessed  b}r  the  various  parts  in  the 
absorption  of  such  matters. 

1244.  Effects  of  mechanical  injuries  upon  the  plant.     The  most 
important  of  these  are  caused  by  destructive  fungi.     The  destruc- 

1  Wirkung  des  Lichtes  und  der  Warme  auf  Schwarmsporen,  1878,  p.  66. 

2  Untersuchungen  iiber  das  Protoplasma,  1864,  p.  100. 
»  Pflanzenphysiologie,  ii.,  1881,  p.  454. 

*  Pflan/enkrankheiten,  1879. 


LIGHTNING.  477 

tion  primarily  affects  the  cell-contents,  and  later  the  cell-wall. 
It  is  very  highly  probable  that  in  certain  cases  various  pro- 
ducts of  decomposition  arising  from  the  progress  of  the  fungi  may 
themselves  prove  poisonous  to  contiguous  parts  of  the  plant. 

One  of  the  most  important  problems  of  practical  horticulture 
and  agriculture  is  the  search  for  efficient  means  by  which  invad- 
ing fungi  may  be  destroyed  without  at  the  same  time  injuring 
the  host-plant  to  which  they  have  attached  themselves.1 

1245.  The  presence  of  certain  fungi  in  plants  sometimes  gives 
rise  to  abnormal  growths  and  to  various  distortions.     When  once 
their  disturbing  influence  is  felt,  the  subsequent  growth  may  be 
affected  for  a  long  time,  and  the  malformations  become  of  an 
extraordinary  character. 

1246.  Considerable  distortions  are  often  produced  by  bites 
or  other  injuries  by  insects.2    Galls  —  for  instance  those  of  the 
oak  and  willow  —  are  among  the  most  noteworthy  instances  of 
this  kind. 

1247.  The  effects  of  lightning  upon  trees  have  been  examined 
by  many  observers.      Cohn8  and  Colladon*  have  pointed  out 
some  of  the  characteristic  injuries  sustained  by  species  of  poplar, 
elm,  and  oak,  stating  that  the  stroke  does  not  usually  affect  the 
summit  of  the  first  two,  but  that  oaks  are  frequently  struck  at 
their  uppermost  branches.     The  course  of  the  injury  is  often 
spiral,  winding  around  the  trunk  in  stripes  which  involve  part  of 
the  sap-wood  and  bark. 

It  is  not  now  believed  that  any  species  of  trees  are  exempt 
from  injury  from  lightning,  although  the  ash  was  formerly 
thought  to "  possess  a  remarkable  degree  of  immunity. 

1248.  Partial  or  complete  blanching  of  otherwise  healthy  leaves 
exposed  to  light  has  been  regarded  by  some  observers  as  an  indi- 
cation of  a  diseased  condition.     In  some  cases  the  blanching  is 
dependent  upon  a  lack  of  iron  in  the  soil  (see  791),  but  in  others 
it  appears  to  be  strictly  hereditary,  being  propagable  both  by 
bud  and  by  seed.     Nothing  is  known,  however,  as  to  its  causes 
in  these  cases,  and  they  are  generally  referred  to  the  unsatis- 
factory category  of  sports. 

It  is  worthy  of  notice  that  a  considerable  proportion  of  the 
so-called  variegated  plants,  especially  of  those  which  have  only 

1  For  an  account  of  some  experiments  in  this  field,  see  Frank  :  Pflanzen- 
krankheiten,  1879  ;  and  Nobbe :  Handbnch  der  Samenkunde 

2  For  a  bibliography  of  this  subject,  see  Frank's  Pflanzenkrankheiten. 
»  Denkschrift.  d.  Schles.  Ges.  f.  vaterl.  Knit.  Breslau,  1853,  p.  267. 

*  Mem.  de  la  Soc.  de  Phys.  et  d'  Hist.  Nat.  de  Geneve,  1872,  p.  501. 


478  UNTOWARD    INFLUENCES. 

white  spots  intermingled  with  the  green  of  the  leaf,  corne  from 
eastern  Asia,  notably  from  Japan.1 

1249.  The  lease  of  life  of  any  given  plant  is  fixed  primarily 
by  the  inherited  character : 2  hence  we  have  annuals,  biennials, 
and  perennials ;  but  these  differences  are  not  in  all  cases  abso- 
lute, in  some  they  are  even  ill-defined.  The  lease  of  life  is 
modified  secondarily  by  external  influences,  which  have  been 
sufficiently  discussed  in  the  present  volume.  In  conclusion, 
attention  should  be  called  again  to  the  fact  (see  Chapter  V.) 
that  in  man}-  instances  the  duration  of  the  life  of  the  plant  is 
determined  largely  by  mechanical  factors,  especially  the  strength 
of  materials. 


1  Morren  :  Here"dite  de  la  Panachure,  1865,  p.  7 ;  Frank  :  Pflanzenkrank- 
heiten,  p.  465. 

a  The  student  should  examine  Minot  on  "Life  and  Growth," 


GLOSSARIAL  INDEX. 


GLOSSAK1AL  INDEX. 


The  numbers  following  the  titles  refer  to  pages.     An  italicized  page-number 
indicates  that  the  term  which  it  follows  is  denned  on  the  page  to  which  it  refers. 


ABSOLUTE  ALCOHOL  (CtHeO),  use  of, 
as  a  medium,  5,  9. 

Absorption,  chemical,  by  soils,  243;  de- 
pendence of  rate  of,  upon  temperature, 
279;  of  ammonia  by  leaves,  332,  341; 
of  aqueous  vapor  by  leaves,  283;  of 
carbonic  acid  by  plants,  299;  of  gases 
by  water,  300  n. ;  of  liquids  through 
roots,  230;  of  moisture  by  soils,  239; 
of  oxygen  during  germination,  465; 
of  saline  matters  from  soils  by  roots, 
244;  of  water  by  feeds,  463;  of  water 
during  germination,  466;  of  water 
previous  to  metastasis,  267 ;  relation 
of  transpiration  to,  279;  through  the 
cut  end  of  a  stem,  263. 

Absorption-bands,  292,  293. 

Acetic  acid  (HCjHsO2),  as  a  reagent, 
9,  54;  .as  a  mounting-medium  with 
glycerin,  21. 

Achromatin  (a,  without;  xp^na,  color), 
375. 

Acid  azo-rubin,  19. 

Acid  nitrate  of  mercury  (Hg[NOs]2),  13. 

Actinic  rays  of  the  spectrum.  See  Chem- 
ical Rays. 

Active  protein  matters  of  plants,  44. 

Adaptation  of  plants  to  dry  climates, 
280. 

Adenophore  (*&*}*,  a  gland;  <i>opiu>,  I 
bear),  461. 

^Esculin  (Cj,HMO13),  362. 

^Ethalium  septicum,  composition  of  pro- 
toplasm of,  197;  locomotion  of,  397; 
preparation  of  plasmodium  of,  for  ex- 
amination, 196. 

Agamogenesis  (a,  without;  y<if"«,  mar- 
riage ;  y«V«ris,  origin),  426. 

Age  of  trees,  140. 

Aggregation,  340,  343,  421,  n. 


Air,  composition  of,  303;  contained  in  a 
plant,  100 ;  contained  in  fresh  woods, 
261 ;  removal  of,  from  specimens,  9. 

Air-passages,  100. 

Air-plants.     See  Epiphytes. 

Albumen  of  the  seed,  181. 

Albumin,  diffusion  of,  223 ;  of  plants,  363. 

Albuminoids,  325,  n. ;  formation  of,  in 
the  plant,  335 ;  tests  for,  28 ;  transfer 
of,  356. 

Alburnum.    See  Sap-Wood. 

Alcohol  (C2H6O),  action  of,  upon  cer- 
tain parasites  and  saprophytes,  294; 
action  of,  upon  chlorophyll,  41,  290; 
use  of,  as  a  medium,  5;  use  of,  as  a 
preserving  and  hardening  agent,  9; 
use  of,  in  preparation  of  specimens  for 
mounting,  23;  use  of,  in  removing  air 
from  specimens,  9. 

Aldrovanda,  344. 

Aleurone  grains  (a\fvpov,  wheaten  flour), 
47.  See  also  Protein  Granules. 

Algae,  absorption  by,  230;  growth  of 
certain,  at  low  temperatures,  385;  in 
hot  springs,  205. 

Alkaloids,  327,  365 ;  cannot  be  utilized 
bv  plants,  335;  effect  of,  upon  plants, 
365,  476. 

Alkanna  (alkanet  root),  18,  363,  n. 

Alum  (K2A12[SO2]4  +  24  H2O  or  [NH4], 
A1208[S02]4  +  24H,0),  10. 

Aluminium,  occurrence  of ,  in  plants,  256. 

Amides,  occurrence  of,  in  grasses,  336. 

Amidoplasts  (a/ivAov,  starch;  TrWo-w,  I 
form),  name  proposed  by  Errera  for 
leucoplastids. 

Ammonia  (NH4OH),  absorption  of,  by 
leaves,  332,  341;  absorption  of,  by 
soils,  243;  formation  of,  in  putrefac- 
tion, 333. 


31 


482 


GLOSSARIAL   INDEX. 


Ammonia-carmin,  16. 

Amoeboid     movement    of     protoplasm 

(in<H/3>j,  change;  "to,  form),  201. 
Amylogenic  bodies  (iftuAov,  starch;  Y«"- 

vd<a,  I  produce),  43.     See  also  Leuco- 

plastids. 

Amyloid  (a/iuAo»,  starch;  el«o«, form),32,n. 
Anaesthetics,  effect  of,  upon  protoplasmic 

movements,  211;  effect  of,  upon  the 

Sensitive  plant,  424. 
Anaplast  (o^oirXaaau.,  I  shape),  287,  n. 
Androscium    (ainjp,    a    man;     ol«o«,  a 

house),  426. 
Angiosperms    (ary«'o*.    vessel;    <mtpv.a, 

a  seed),  fertilization  in,  426. 
Angle  formed  by  the  union  of  a  branch 

and  the  trunk,  193. 

Anilin  blue,  action  of,  upon  callus,  94. 
Anilin  chloride,  use  of,  as  a  test  for  lig- 

nin,  10,  37. 
Anilin    sulphate   (2  tC8HsNH8]S04Ht), 

use  of,  as  a  test  for  lignin,  10,  37. 
Animals,  occurrence  of  chlorophyll  in, 

288. 
Annual  growth  of  rooto,  114;  of  stems, 

137,  139. 
Annular  markings  (anmtlut,  &  ring),  30, 

85. 
Anther  (i^pd*,  flowery),  development 

of  the,  171. 
Antheridia,  441,  n. 
Antherozoids,  440,  n.,  441,  n. 
Anticlinal  planes  (avri,  against;  «AiV«iv 

[«Aiv»],  to  incline),  382. 
Antipodal  cells  (*vri,  against;  wotf*,  a 

foot),  434. 
Apheliotropic    curvatures    (aird,    from; 

»>AI<K,  the  sun ;  rp6*os,  a  turn),  393. 
Apical  cell  in  roots  of  the  higher  crypto- 
gams, 117. 

Apogamy    (0*0,    without;    YO.AW.  mar- 
riage), 446. 
Apogeotropic  organs  (aird,  from;  m,  the 

earth;  rpoiros,  a  turn),  392. 
Apospory  (<iird,  without;  <nrdp<K,  seed), 

the  substitution,  in  reproduction,  of 

budding  for  asexual  spore-formation. 
Apostrophe  (aird,  from;  <npo<K  a  turn- 
ing), 399. 
Apposition  theory  concerning  the  growth 

of  the  cell-wall,  219. 
'Approach  grafting,  152. 
Aquatics,  absorption  by,  230 ;  epidermis 

of,  67. 

Aqueous  tissue.     See  Water  Tissue. 
Arabin  (2CeH100»-(-H20),  358. 
Archegonium,  441,  n.,  442,  n.,  443,  n. 


Archesporium  (tpxi,  beginning;  <nrdpo«, 
seed),  777,  n.,  379. 

Areolated  dots  (oreofct,  a  small,  open 
place),  30,  82. 

Argentic  ni'rate  (AgNCM,  10. 

Arsenic,  occurrence  of,  in  plants,  256 ;  use 
of  compounds  of,  as  insecticides,  476. 

Artificial  cell,  226. 

Asexual  reproduction,  426,  444. 

Ash,  amountof,in  plants,  236,247;  compo- 
sition of,  in  plants,  247 ;  of  autumn  and 
spring  leaves  compared,  281;  office  of 
the  different  constituents  in  plants,  252. 

Asparagin  (C«H8N1O,+  H,O),  10,  364, 
372. 

Asphalt-cement,  20,  24. 

Assimilating  system  of  the  plant,  285. 

Assimilation,  185,  284;  a  process  of  re- 
duction, 285,  320;  diloroplijll  acts  as 
a  screen  in,  323;  conditions  for,  285; 
contrasted  with  respiration,  356 ;  course 
of  transfer  of  the  products  of,  356; 
Draper's  experiments  upon,  310;  early 
history  of,  323;  effect  of  artificial  light 
upon,  316;  formic  aldehyde  hypothe- 
sis, 322;  free  oxygen  not  necessary 
for,  318;  influence  of  colored  light 
upon,  310;  measure  of  activity  of,  by 
the  bacterial  method,  315;  measure- 
ment of  the  amount  of,  312;  portion 
of  the  spectrum  causing  maximum 
activity  in,  314;  practical  study  of, 
305;  products  of,  320;  products  of, 
necessary  for  growth,  384 ;  raw  ma- 
terials required  for,  299;  relations  of 
carbonic  acid  to,  318;  relations  of  tem- 
perature to,  316 ;  storing  of  products 
of,  in  perennials,  373. 

Atavism  (atavus,  an  ancestor),  447. 

Atom,  213,  n. 

Auric  chloride  (AuCl,),  10. 

Automatic  (autonomic)  movements,  413. 

Autoplast  (ai.T<k,  self;  irAa*™,  I  form), 
287,  n. 

Autumn  wood,  138,  395. 

Autumnal  changes  in  color  in  leaves, 
297. 

Auxanometers  (aOfr)<ri«,  increase ;  /"'TPOK. 
measure),  383. 


BACTERIA,  measurement  of  activity  of 

assimilation  by,  315. 
Balsam.  Canada,  22;  Copaiba,  363;  of 

Fir,  363;  of  Peru,  363;  of  Tolu,  368. 
Balsams,  97,  3«3. 
Barium,  occurrence  of,  in  plants,  256. 


GLOSSARIAL   INDEX. 


483 


Bark.  147,  149. 

Basifugal  growth  (basis,  base;  /woo,  I 
flee),  156. 

Basipetal  growth  (basis,  base;  peto,  I 
move  toward),  156. 

Bassorin  (CeH,005),  358. 

Bast-fibres,  87 ;  clinging  together  of,  in 
inner  bark,  147;  in  cribose  portions  of 
fibre-vascular  bundles,  104;  forming 
sheaths  of  collateral  bundles,  123;  re- 
actions of,  90;  separation  of,  from  the 
stem,  147;  size  of,  90;  solubility  of, 
33,  «. ;  strength  of,  189. 

Beale's  carmin,  17. 

Benzol  (CgHJ,  a  solvent  for  fats,  10; 
use  of,  in  preparation  of  specimens 
for  mounting,  23 ;  use  of,  in  section- 
cutting,  3;  use  of,  in  treatment  of  the 
chlorophyll  pigment,  291. 

Benzol-balsam,  23. 

Bibulous  paper,  use  of,  5. 

Bid, llateral  bundles,  104 ;  in  stems, 
123. 

Bifacial  arrangement  of  leaf-parenchy- 
ma, 158. 

Biforines  (biforu,  having  two  doors), 
53,  n. 

Blanching  of  leaves,  254,  297,  477. 

Blastocolla  (0*<«™>s,  shoot;  «dMa,  glue), 
the  balsam  produced  on  buds  by  glan- 
dular hairs. 

Bleaching  processes,  11. 

Bleeding  of  plants,  264. 

Bloom,  67,  294. 

Bordered  pits,  30,  82. 

Boron,  occurrence  of,  in  plants,  256. 

Branches,  rudimentary  and  transformed, 
153. 

Branching  of  roots,  115,  232. 

Bristles,  69. 

Bromine,  occurrence  of,  in  plants,  256. 

Brownian  movement,  429. 

Budding,  152,  444. 

Buds  on  leaves,  162. 

Bud-variations,  444. 

Bundle-sheath,  104. 

Burnettizing,  142. 

Byblis,  345. 

CESIUM,  occurrence  of,  in  plants,  256. 

Caffeine  (CgH10N4(X),  327. 

Calcareous  soils,  239. 

Calcic  chloride  (CaCl2).  use  of,  as  a 
clearing  agent,  10 :  use  of,  as  a  mount- 
ing medium,  21 ;  use  of,  in  the  meas- 
urement of  transpiration,  274. 


Calcic  hypochlorite  (CaCl202).  use  of,  as 
a  bleaching  agent,  11. 

Calcium,  occurrence  of  compounds  of,  in 
plants,  39,  54,  247,  337;  office  of,  and 
its  compounds  in  the  plant,  253. 

Callus,  as  a  means  of  healing  plant 
wounds,  150 ;  in  sieve-cells.  93. 

Calyptrogen  (icnAum-pa,  a  cover;  yewaia, 
I  produce),  107,  n. 

Cambiform  cells,  122. 

Cambium,  104,  123,  735,  136;  cell- 
division  in,  377. 

Cambium-ring,  137. 

Cambium  fibres,  81,  n. 

Camera  lucida,  4. 

Camphors,  363. 

Canada  balsam,  22. 

Cane-sugar  (C12H22OU),  amount  of,  in 
plants,  359 ;  diffusion  of,  223 ;  test 
for,  52. 

Capillary  water,  242. 

Caramel,  diffusion  of,  222,  223. 

Carbohydrates,  51, 357;  transfer  of,  356. 

Carbolic  acid  (C8H6 .  OH),  use  of,  as  a 
clearing  agent,  167;  use  of,  as  a  test 
for  lignin,  11,  37. 

Carbon,  appropriation  of,  by  plants, 
285 

Carbon  disulphide  (CS,),  11. 

Carbonates,  test  for,  9,  54. 

Carbonic  acid  (used  in  this  work  as  a 
term  for  carbon  dioxide,  C02),  absorp- 
tion of,  by  plants,  299,  305;  amount 
of,  decomposed  in  assimilation,  319; 
amount  of,  decomposed  by  plants  pro- 
portional to  the  distribution  of  effective 
caloric  energy  in  light,  314;  amount 
of,  in  natural  waters,  300 ;  amount  of, 
in  rain-water,  299,  300,  n.;  amount  of, 
most  favorable  to  assimilation,  319; 
effect  of  a  large  supply  of,  upon  vege- 
tation, 304,  318 ;  roots  do  not  take  up, 
300. 

Carmin,  16;  with  picric  ncid,  17. 

Carnivorous  plants,  338. 

Carpogonium,  440,  ». 

Carpophytes,  reproduction  in,  440,  n. 

Casein  of  plants,  363. 

Castor-oil,  use  of,  as  a  medium,  5. 

Caulicle  (cnuliculus,  a  small  stem),  403 ; 
movements  of  the,  403;  sensitiveness 
of  the,  415;  structure  of  the,  106,  118. 

Caustic  soda.    See  Sodic  Hydrate. 

Cell,  25;  an  osmotic  apparatus,  229; 
origin  of  name,  25. 

Cell-division,  374:  directions  of,  380; 
in  plant-hairs,  380;  in  the  cambium 


484 


GLOSSARlAL 


of  Pinus,  377 ;  in  the  development  of 
pollen-grains,  379 ;  in  the  formation 
of  stomata,  376 ;  method  of  demonstra- 
tion of,  380. 

Cell-plate,  376. 

Cell-sap,  carbohydrates  in  the,  51 ;  color 
of  the,  in  flowers,  170;  color  of  the, 
masks  that  of  chlorophyll,  294. 

Cells,  animal,  analogous  to  vegetable, 
220 ;  classification  of,  56,  59 ;  develop- 
ment of,  58;  method  of  determining 
the  density  of  the  contents  of,  390; 
morphological  changes  in,  during 
growth,  373;  turgiditv  of  newly 
formed,  389. 

Cellular  system,  57,  60,  102. 

Cellulose  (C<jHioO»),  composition  of,  31; 
formation  of,  in  cell-division,  376 ;  oc- 
currence of,  with  crystals,  54;  rela- 
tions of,  to  moisture,  219;  solubility  of 
the  modifications  of,  33,  n.,  35,  n. ;  spe- 
cific gravity  of,  145;  stability  of,  354, 
357;  tests  for,  8,  11,  15,  31.  .See  also 
Cell-wall. 

Cell-wall,  capacity  of  the,  for  transfer 
of  water,  258  ;  direction  in  which  the, 
is  laid  down,  380;  formation  of,  29, 
218;  growth  of.  218,  355;  markings 
of  the,  29;  modifications  of  the,  34; 
plates  of  the,  in  cork-cells,  38;  rela- 
tions of  the,  to  protoplasm,  218;  rela- 
tive amount  of  space  occupied  by  the, 
in  fresh  wood,  261;  structure  of,  29, 
257;  tensions  in  the,  390. 

Central  cylinder,  changes  in  the,  113; 
structure  of  the,  110. 

Centric  arrangement  of  leaf -parenchyma, 
158. 

Cerasin,  358. 

Chemical  absorption  by  soils,  243. 

Chemical  rays  of  the  spectrum,  308;  least 
efficient  in  assimilation,  310,  311,  313. 

Cherry-wood,  use  of,  in  testing  for  lig- 
nin,"  14. 

Chloral  hydrate  (CC1,CH[OH],),  11,  42. 

Chlorine,  occurrence  of,  in  plants,  247; 
office  of,  in  the  plant,  254. 

Chloroform  (CHCI,),  effect  of,  upon 
protoplasmic  movements,  211 ;  effect 
of,  upon  the  Sensitive  plant,  424;  use 
of,  in  preparation  of  specimens  for 
mounting,  23. 

Chloroform-balsam,  23. 

Chloroiodide  of  zinc,  8,  33. 

Chloroleucites.     See  Chloroplastids. 

Chlorophyll  body  (x*"/**,  green ;  4>vAAoi>, 
leaf),  41. 


Chlorophyll  granules,  26,  41,  286;  actiort 
of  alcohol  upon,  41 ;  action  of  darkness 
upon,  42;  action  of  hydrochloric 
acid  upon,  290,  475,  n.;  action  of 
steam  upon,  290,  475,  ». ;  action  of 
various  agents  upon,  474,  n. ;  break- 
ing up  of,  at  autumn,  298 ;  formation 
of,  287;  in  epidermal  cells,  67;  in 
evergreen  leaves,  298 ;  occurrence  of, 
288;  position  of  the,  during  the  day 
and  at  night,  398  ;  Pringsheim's  study 
of,  13,  289 ;  stroma  of,  290 ;  structure 
of,  289. 

Chlorophyll  pigment,  41,  286;  absence 
of,  in  certain  plants,  294;  changes  in 
the,  at  autumn,  297;  color  of  a  solu- 
tion of  the,  not  permanent,  296;  ex- 
traction of  the,  290;  fluorescence  of 
the,  294;  in  Florideae,  295;  spectrum 
of  the,  292,  313. 

Chlorophyllan,  291,  n.,  292,  n. 

Chloroplastids  (X^PO*.  green;  irA«£<r<r<o, 
I  form),  41.  See  also  Chlorophyll 
Granules. 

Chlorosis,  297. 

Chromatin  (XP"^^  color),  375,  378. 

Chromatophores  (XP^MI  [gen.  xp<«W™«], 
color;  <t»opi<a,  I  bear),  41.  n.,  287,  n. 

Chromic  acid  (CrOs),  action  of,  upon 
the  cell-wall,  11,  39. 

Chromoleucites.     See  Chromoplastids. 

Chromoplastids  (xfx-W.  color;  irA<«r<ra», 
I  form),  41,  287. 

Cilia  (cilium,  an  evelash),  movements 
by  means  of,  398. 

Cinchona,  bast-fibres  of,  148,  n. 

Circumnutation  (circum,  around;  nuta- 
tio,  a  nodding),  400 ;  in  seedlings.  403; 
methods  of  observation  of,  401 :  modi- 
fied, 401,  407;  of  the  radicle,  403,  415; 
of  tendrils,  417;  of  the  young  parts  of 
mature  plants,  405. 

Citric  acid  (CeHgO,),  360. 

Clathrate  cells  (clathri,  a  lattice),  the 
name  given  bv  Mohl  to  cribriform 
cells. 

Clayey  soil,  238. 

Clearing  agents,  7,  10,  11. 

Cleft  of  a  stoina,  269. 

Climate,  adaptations  of  plants  to  a  drv, 
280. 

Climbing  plants,  406. 

Clinostat  («Xiw*,  I  incline;  <rrar6t. 
placed),  408. 

Close-fertilization,  447;  results  of,  con- 
trasted with  those  of  cross-fertilization, 
448. 


GLOSSARIAL  INDEX. 


485 


Closed  bundles,  104,  128. 

Coal-tar  colors,  18,  39. 

Cobalt,  occurrence  of,  in  plants,  256. 

Cochineal,  18. 

Cold,  effects  of,  upon  plants,  471. 

Coleorhiza  (<coA«6*,  sheath;  p'ifr,  root), 
107,  n. 

Collateral  bundles,  structures  of,  104, 
121. 

Collenchyma  («oAAa,  glue;  «YX"MO,  an 
infusion),  64;  in  roots,  110;  strength 
of,  191. 

Colloids  (KoAAa,  glue;  «Wo«,  like),  222, 
223,  n. 

"Colored"  plants,  294. 

Colors,  as  nectar  guides,  453 ;  of  flowers, 
170,  453;  of  fruits,  177;  of  plants  de- 
veloped in  darkness,  288;  of  seeds, 
178 ;  of  woods,  141. 

Community  in  plants,  425. 

Compass  plant,  arrangement  of  paren- 
chyma in  leaf  of  the,  160. 

Complete  oxidation,  355. 

Compound  hairs,  68. 

Compound  microscope,  1. 

Compound  pistils,  173. 

Concentric  bundles,  structure  of,  104, 
123. 

Concentric  rings  in  roots  of  annuals,  115. 

Conductive  tissue  of  the  ovary,  432 ;  of 
the  style,  431. 

Conglutin,  363. 

Coniferin  (C18HWO8  +  2H,O),  362. 

Consanguinity,  fertilization  in  different 
degrees  of,  446. 

Continuity  of  protoplasm  in  cells,  214. 

Copper,  occurrence  of,  in  plants,  256. 

Copper  salts,  use  of,  in  making  precipi- 
tation-membranes, 225. 

Corallin  (C*,H160S),  15. 

Cork,  as  a  means  of  healing  plant- 
wounds,  150;  character  of  cell-walls 
of,  75 ;  color  of  cells  of,  76 ;  formation 
of  cells  of,  75;  origin  and  formation 
of,  74,  148;  reaction  of,  with  iodine, 
34,  n. 

Cork  cambium.     See  Phellogen. 

Cork-cortex  cells,  148.  n. 

Cork  meristem.    See  Phellogen. 

Corpuscles  (corpusculum,  a  little  body), 
438. 

Corrosion  by  roots,  246. 

Corrosive  sublimate.  See  Mercuric  Chlo- 
ride. 

Cortex  (cortex,  the  bark),  in  parasitic 
roots,  116  ;  in  roots,  110,  113 ;  in 
stems,  119. 


Cortical  sheath,  a  term  applied  by  Na- 
geli  to  the  whole  of  the  primary  bast- 
bundles. 

Cotton,  179. 

Cotton-blue  "B,"  19. 

Cover-glasses,  4,  6. 

Creosoting,  142. 

Cribriform  tissue  (cribrum,  sieve ;  forma, 
form),  91. 

Cribrose-cells.     See  Sieve-cells. 

Cross-breed,  455. 

Cross-fertilization,  447;  results  of,  con- 
trasted with  those  of  close-fertilization, 
448. 

Crown  of  the  root,  153. 

Cryptogams,  reproduction  in,  439,  n.; 
roots  of,  116;  stems  of,  154. 

Crystal-cells,  97. 

Crystalloids  ((cpvoraAAos,  a  crystal;  el&os, 
form),  45,  47,  183. 

Crystalloids  in  diffusion,  222. 

Crystals,  composition  of  plant,  54;  for- 
mation of,  by  Vesque's  method,  55; 
forms  of  plant,  52 ;  in  bast,  89,  147 ; 
occurrence  of,  in  plants,  52,  54,  ». 

Cultivated  plants,  supply  of  nitrogen  to, 
334. 

Cuprammonia  (Cu2[NH4]0,),  11. 

Cupric  acetate  (Cu[C2Hs02],),  use  of,  in 
examination  of  resins,  12. 

Cupric  sulphate  (CuSO«),  12. 

Curvature  of  concussion,  390. 

Cuticle  (cuticula,  the  skin),  65;  solubil- 
ity of,  34, ». 

Cuticularization.    See  Cutinization. 

Cuticularized  layers,  66. 

Cutin  (cutis,  skin),  38. 

Cutinization,  34,  38. 

Cutose,  35, ». 

Cyanic  flower  colors  (*vavos,  dark  blue), 
"454. 

Cystoliths  («wm«,  bladder ;  Ai*o»,  a 
stone),  40. 


DAMAK,  23,  380. 

Darkness,  color  of  plants  developed  in, 
288 ;  effect  of,  upon  opening  and  clos- 
ing of  stomata,  270;  effect  of,  upon 
protoplasmic  movements,  206. 

Darlingtonia,  349. 

Defoliation,  163. 

Degradation  changes  in  the  cell-wall,  40. 

Degradation  products,  40,  362. 

Density  of  wood,  144. 

Depth  to  which  roots  branch,  233. 

Derivative  hybrids,  458. 


486 


GLOSSARIAL   INDEX. 


Dermatogen  (fiep^a  [gen.  ««PM«T<K],  skin; 
ycKvaw,  I  produce),  705, 118,  155. 

Desmids,  movements  of,  398. 

Desmodium  gyrans,  413. 

Dextrin  (CoH.'oO,,),  51,  358. 

Dextrose.    See  Grape-sugar. 

Diageotropic  organs  (S"i,  through;  y>?, 
the  earth;  rpoiro*,  a  turn),  392. 

Diaphragms,  for  controlling  the  illumi- 
nation of  microscopic  objects,  2;  of  air- 
passages,  100. 

Diastase  (iia<rra<rif,  separation),  468. 

Diatoms,  movements  of,  398. 

Dicotyledons  (to,  twice;  «oTvAij&ii-,  a 
cup-shaped  hollow),  distribution  of 
mechanical  elements  in,  193;  secon- 
dary structure  of  steins  of,  136 ;  stems 
of,  129. 

Diffusion,  laws  of,  222;  of  liquids,  221; 
of  gases,  301. 

Dionaea  muscipula,  342;  related  to  Dro- 
sera,  351. 

Dipsacus,  350. 

Discoid  markings  (Ji'o-xot,  a  round  plate; 
ttt<K,  form),  30,  82. 

Diseases  of  plants,  470. 

Dissecting  instruments,  2. 

Distances  to  which  roots  extend,  235. 

Division  of  labor  in  the  plant,  185. 

Double-staining,  19. 

Drainage  of  soiU,  amount  of  solid  mat- 
tt-r  dissolved  in  water  from,  244;  rela-    | 
tions  of  rain-fall  to,  242. 

Drawing  of  preparations,  4. 

Drawn  shoots,  388. 

Drosera  rotundifolia,  339;  related  to 
Dionaea,  351. 

Drosophyllum,  345. 

Dry  mounts,  20. 

Ducts.    See  Vessels. 

Duramen  (durare,  to  harden).  See 
Heartwood . 

Dwelling-houses,  plants  in,  868. 


EARTH-WORMS,  influence  of,  upon  the 
character  of  the  soil,  239. 

Egg-apparatus,  435. 

Electricity,  effect  of,  in  forming  nitrogen 
compounds  in  the  atmosphere,  332; 
relations  of  protoplasm  to,  207. 

Electric  light,  effect  of,  upon  assimila- 
tion, 316. 

Embryo,  life  of  the,  469. 

Embryo-sac,  434. 

Enchylema  (iy\*«,  I  pour  in),  198. 


Endodermis  (ivtoi;  within;  Upfio,  the 
skin),  63,  104,  110,  120. 

Endogenous  stems  (iv6ov,  within ;  ytwau, 
I  produce),  129. 

Endopleura  (iv&ov,  within;  wAevpo,  the 
side),  178. 

Endosmose  (iv&ov,  within;  wo>6?,  a 
thrusting),  229. 

Endosperm  (ev&ov,  within;  viripna.,  seed), 
437. 

Energy,  307,  322 ;  supply  of,  for  work, 
354.' 

Eosin  (C»H,Br4Os),  19. 

Epiblema  (iiri/SAWa,  a  cloak),  230. 

Epicotyl  («»i,  upon ;  KOTVA>J,  a  cup),  403. 

Epidermal  spines,  69. 

Epidermal  system,  102. 

Epidermis  («"',  upon;  Sep^a,  the  skin), 
58,  64;  cells  of,  65;  diffusion  of  gases 
through,  302;  multiple,  67;  of  the 
flower,  170;  of  the  leaf,  161;  of  the 
ovary,  172;  of  the  stem,  119;  waxy 
coatings  upon  the,  66. 

Epinastic  curvature  (««•'',  upon;  vaarot, 
pressed  close),  408. 

Epiphytes  (««',  upon;  4>vr6v,  a  plant), 
352." 

Episperm  («»«',  upon;  <rir«p/aia,  seed),  178. 

Epistrophe  (ttriorpo^jj),  a  turning  about, 
399. 

Epithelium  of  air-spaces  («»«,  upon ;  *>)A>j, 
nipple),  101. 

Equilibrium  of  water  in  the  cell,  258. 

Equisetum  (equus,  a  horse;  saeta  [«i/a], 
hair),  epidermis  of,  154;  stem  of.  J54. 

Erythrophyll  («pvflp<k,  red;  <t>vMov,  leaf), 
291,  n.;  297. 

Ether  (C4HIOO),  effect  of,  upon  proto- 
plasmic movements,  211;  a  solvent 
for  fats,  12. 

Ether  (of  space),  306. 

Ethereal  oils,  362. 

Etiolation,  288,  291,  295,  388. 

Etiolin,  291;  spectrum  of,  29(5. 

Evaporation,  compared  with  transpira- 
tion, 275;  from  an  animal  membrane, 
275 ;  from  soils,  241 :  from  the  surface 
of  a  plant,  257;  relation  of  growth 
to,  271,  n. ;  relation  of  rain-fall  to, 
242. 

Evergreen  leaves,  164 ;  changes  of  chlo- 
rophyll granules  in,  at  autumn,  298. 

Exine.    See  Extine. 

Exogenous  stems  («"£•>,  outside;  ytvv**>, 
I  produce),  129. 

Exosmose  (<(u>,  outside ;  wr/iof ,  a  thrust- 
ing),  229. 


GLOSSARIAL  INDEX. 


487 


Extine  (exter,  on  the  outside),  428. 
Exudation  of  water  from  uninjured  parts 

of  plants,  267. 
Eye-pieces,  2. 


FALL  of  the  leaf,  162,  217. 

Fascicles  of  mosses  (fascicvlut,  a  small 
bundle),  155. 

Fascicular  system,  102. 

Fats,  occurrence  of.  in  plants,  360:  sol- 
vents for,  10,  11,  12. 

Fermentation,  333,  n.,  369,  n.,  372. 

Ferments,  326,  365,  467. 

Ferns,  epidermis  of,  154;  reproduction  in, 
442,  446;  stems  of,  154. 

Ferric  acetate  (Fe[C,H,O,]6)  used  as  a 
test  for  tannin,  12. 

Ferric  chloride  (Fe,Cl«)  used  as  a  test 
for  tannin,  12. 

Ferric  sulphate  (Fe,[SO«]s)  used  as  a 
test  for  taunin,  12. 

Fertilization,  close,  447;  cross,  447; 
grades  of  partial,  456;  in  angiosperms, 
435;  in  different  degrees  of  consan- 
guinity, 446;  in  gymnosperms,  437; 
in  hybrids,  456;  results  of  different 
methods  of,  contrasted,  448. 

Fibres  (/6m,  a  fibre),  57,  79;  bast,  87 ; 
cambium,  81;  liber,  87;  libriform,  80; 
septate,  80;  substitute,  80;  woody, 
80. 

Fibro-vascular  bundles  (fbra,  a  fibre; 
vasculum,  a  small  vessel),  103;  bicol- 
lateral,  104;  closed,  104,  128;  col- 
lateral, 104,  121;  concentric,  104; 
parts  of,  104,  111 ;  course  of,  105,  125; 
distribution  of,  in  dicotyledons,  130; 
distribution  of,  in  palms,  127.  130, 
131,  n.;  formation  of,  136,  137;  in  the 
flower,  170;  in  the  leaf,  156;  in  the 
ovary,  172;  in  the  stem,  120;  number 
of,  in  the  central  cylinder,  111;  open, 
104;  radial,  104;  relation  of  the  num- 
ber of,  in  the  leaves  to  the  number  of, 
in  the  stem,  125. 

Fibro-vascular  system,  57,  103. 

Filtering-paper,  use  of,  5. 

Filtration  through  soils,  243. 

Fire-weeds,  469. 

Fixed  air,  304. 

Floral  clock,  412. 

Floridese,  coloring-matters  of,  295. 

Flowers,  colors  of,  170,  453;  develop- 
ment of,  166  ;  odors  of,  454 ;  regarded 
as  modified  branches,  166;  times  of 
opening  and  closing  of,  412. 


Fluorescence  of  the  chlorophyll  pigment, 

Fluorine,  occurrence  of,  in  plants,  256. 

Foliar  trace  (folium,  a  leaf),  125. 

Food,  effects  of  improper,  upon  plants, 
473;  materials  for,  in  seeds,  182,  437, 
467;  methods  of  utilization  of,  354. 

Foramen  of  the  ovule,  175. 

Force  exerted  during  growth,  395. 

Forcing,  444. 

Forests,  effect  of,  upon  the  amount  of 
water  in  the  soil,  283 ;  effect  of,  upon 
rain-fall,  282;  humidity  of,  281. 

Formic  aldehyde  (CH2O)  hypothesis  in 
assimilation,  322. 

Forms  of  life  of  the  plant,  470. 

Fovilla  (foveo,  I  cherish),  429. 

Franchimont's  test  for  resins,  12. 

Fraunhofer's  lines,  293. 

Free  nitrogen  not  available  to  plants, 
327. 

Free  veins  in  leaves,  167. 

Fremy's  process  for  extraction  of  the 
chlorophyll  pigment,  290. 

Frey's  glycerin-carmin,  17. 

Fronds  of  the  palm-stem  (from,  a  leafy 
branch),  131. 

Frost,  effect  of,  upon  plants,  471;  not 
necessary  to  the  production  of  the  au- 
tumnal changes  of  color  in  leaves, 
298. 

Fruits,  changes  in  the  ripening  of,  460; 
classification  of  explosive,  400 ;  color- 
ing-matters of,  177;  fastening  of,  in 
the  soil  by  hygroscopic  movements, 
399;  hard  parts  of,  176;  movements 
due  to  changes  in  ripening  of,  400 ; 
nature  of,  176. 

Fruit-sugar,  359. 

Fundamental  cells,  56,  60. 

Fundamental  system.  -See  Cellular  Sys- 
tem. 

Fungi,  injuries  to  plants  by,  474,  476; 
solutions  for  cultivation  of,  251, ». 

Funiculus  (funiculus,  a  slender  cord), 
175. 


GALLIC  ACID  (CrH,Oj),  361. 

Gamogenesis  (y«4*o«,  marriage; 
formation),  426. 

Gases,  absorption  of,  by  water,  300,  «.; 
condensation  of,  by  soils,  244;  diffu- 
sion of,  301 ;  effect  of  noxious,  upon 
plants,  473;  effect  of  various,  upon 
growth,  384:  in  rain-water,  300,  n.; 
passage  of,  through  epidermis  free 


488 


GLOSSARIAL   INDEX. 


from  stomata,  302 ;  passage  of,  through 
stomata,  303;  proportions  of  various, 
in  the  air,  303 ;  relations  of  protoplasm 
to  various,  210. 

Gelatin,  of  plants,  364;  tannate  of,  226. 

Gelatination,  34. 

Genera,  447. 

Genlisea,  346. 

Gentian-violet,  380. 

Geotropic  organs  (m,  the  earth;  rpdiro?, 
a  turn),  392. 

Geotropism,  392. 

Gerlach's  ammonia-carmin,  16. 

Germination,  changes  during,  468;  con- 
ditions of,  462;  not  hastened  by  chem- 
ical means,  468;  of  oily  seeds,  368, 
468 ;  phenomena  of,  466 ;  relations  of, 
to  light,  466;  relations  of,  to  tempera- 
ture, 464;  stages  in,  462,  «.;  time  re- 
quired for,  at  various  temperatures, 
466;  when  complete,  462. 

Girdling  of  steins,  258. 

Glaciers,  aid  of,  in  the  formation  and 
distribution  of  soils,  238. 

Glands,  nectar,  451 ;  of  the  Drosera  leaf, 
339  r  of  leaves,  161. 

Glandular  hairs,  68. 

Gliadin,  364. 

Globoids  (globut,  a  round  body)  47 

Glucose  (CeH^Ot),  52,  359;  held  to  be 
the  first  product  of  assimilation,  322. 

Glucoside,  292,  n.,  362. 

Gluten-casein,  363. 

Gluten-fibrin,  364. 

Glycerides.    See  Fats. 

Glycerin,  effect  of,  upon  protoplasm  in 
cells,  199;  use  of,  as  a  medium  in  mi- 
croscope work,  5 ;  use  of,  as  a  pre- 
servative medium,  21 ;  use  of,  as  a  re- 
agent, 12. 

Glycerin  ethers,  360. 

Glycerin-jelly,  22. 

Gold  orange,  19. 

Gold-size,  24. 

Graft-hybrids,  445. 

Grafting,  152,  444. 

Grains  of  the  cereals,  181. 

Granulose  (grnnulum,  a  small  grain), 
50. 

Grape-sugar,  359.    See  also  Glucose. 

Gravelly  soil,  238. 

Great  curve  of  growth,  389. 

Green,  brilliant,  19 ;  emerald,  19 ;  met h yl, 
19. 

Green  chlorophyll,  322. 

Grenacher's  alum-carmin,  17. 

Growing-point,  106. 


Growth,  355,373;  assumption  of  definite 
form  during,  394;  basifugal,  156; 
basipetal,  15(5 ;  changes  which  accom- 
pany, 373;  conditions  of,  384;  direc- 
tion of,  392;  effects  of  atmospheric 
pressure  upon,  389;  effects  of  gases 
upon,  384;  effects  of  light  upon,  387, 
392;  effects  of  temperature  upon,  385; 
external  pressure  retards,  395;  force 
exerted  during,  395;  great  curve  of, 
389 ;  instances  of  rapid,  384 ;  in  what 
it  consists,  373 ;  measurement  of,  383 ; 
not  always  associated  with  increase  of 
weight,  373;  observation  of,  374;  of 
the  cell-wall,  218,  382;  of  the  leaf, 
155;  periodical  changes  in  rate  of, 
389;  planes  of  walls  at  point  of,  381; 
relations  of  oxygen  to,  388. 

Guardian  cells,  70;  development  of,  376; 
mechanism  of,  269. 

Gum-resins,  98. 

Gums,  51,  358;  diffusion  of,  222,  n. 

Gymnosperms  (yvnv<x,  naked;  <nr*pna.t 
seed),  426,  437. 

Gynoecium  (yvnj,  a  woman;  ol*o«,  a 
house),  426. 


H.«MATOXYLIN  (C,«HUO«  -f  3H,O),  18, 
46,  211,  380. 

Hairs,  68;  cell-division  in,  380;  com- 
pound, 68;  occurrence  of,  in  air-pas- 
sages, 100;  of  seed-coat,  179;  simple, 
68;  used  in  study  of  protoplasm,  198. 

Hales,  device  of,  for  noting  the  growth  of 
a  leaf,  156 ;  experiments  of,  upon  trans- 
piration, 271;  observations  of,  upon 
the  transfer  of  water  through  the 
stem,  258. 

Hartig'scarmin,  16. 

Healing  of  plant-wounds,  150. 

Heart-wood  (Duramen),  141. 

Heat,  absorption  of,  by  soils,  245 ;  effect 
of,  upon  the  direction  of  growth,  394; 
effect  of,  upon  opening  and  closing  of 
stomata,  270;  effect  of,  upon  transpi- 
ration, 277;  effect  of,  upon  vitality  of 
seeds,  205;  evolution  of,  during  res- 
piration, 370 ;  relations  of,  to  germina- 
tion, 464 ;  relations  of,  to  protoplasm, 
201.  See  also  Temperature. 

Heat-rays  of  the  spectrum,  308. 

Heliotropic  curvatures  (fjAios,  the  sun; 
rpoiro?,  a  turn),  393. 

Heliotropism,  392. 

Hepatics,  absorbing  organs  in,  117. 

Heterogeneous  pith,  124- 


GLOSSARIAL   INDEX. 


Hilum  (hilum,  a  little  thing),  48. 
Hohnel's  tests  for  lignin,  10,  14. 
Homogeneous  pith,  124. 
Honey  of  flower,  451. 
Hot  springs,  occurrence  of  plants  in,  205. 
Hoyer's  mounting-media,  23. 
Humus,  337,  n. 
Humus-plants,  337. 
Humus  soils,  239. 

Hybridization,  447,  455;  reciprocal,  455. 
Hybrids,  455;  derivative,  458;  produc- 
tion of  artificial,  453;  strength  of,  458; 

tendency  of,  to  vary,  458. 
Hydrochloric  acid  (HC1),  12;  diffusion 

of,  223;   used  in  the  examination  of 

chlorophyll  granules,    12,   290;   used 

in  the  examination  of  plant-crystals, 

54. 

Hydrostatic  water,  242. 
Hydrotropism    (v&up,   water;    rpoww,  a 

turn),  393. 
Hygroscopic ity   (i>yp6<,   wet;    <«<,.*«,  I 

look  at),  239. 

Hygroscopic  movements,  399. 
Hygroscopic  water,  242. 
Hypochlorin    (vv6\\a>po^,  greenish  yel- 

"low),  290,  322. 
Hypocotyl  (i>ird,  under;  «OTI>AT),  a  cup). 

See  Caulicle. 
Hypoderma  (iuro,  under;  Sip^a,  the  skin), 

119. 
Hyponastic  curvature  (i>iro,  under;  pcurrot, 

close-pressed),  408. 
Hysterogenic  intercellular  spaces  (u<rr«- 

po«,  after;  ytwau,  I  produce),  99,  n. 


IDIOBLASTS    (Mio«,    peculiar; 

offshoot),  69,  n.,  97. 
Inclination  of  the  wood  elements  to  the 

axes  of  trees,  143. 
Individual,  425. 

Indol  (CI6H,4N,),  use  of,  as  a  test  for  lig- 
nin, 13,  37. 
Inferior  ovaries,  arrangement  of  fibro- 

vascular  bundles  in,  174. 
Initial  cells,  105. 
Injuries,  of  the  stem,  149;  to  the  plant, 

470. 
Insectivorous  plants,  338 ;  list  of  works 

relating  to,  351. 
Integuments  of  the  seed,  178. 
Intercellular  spaces,  60,  99 ;  modes  of 

development    of,    99;    occurrence    of 

protoplasm  in,  217. 
Intermediate  zone,  134. 
Internal  glands,  100. 


Internodes,  characteristics  of  growing, 
390;  movement  in  twining  plants  of 
young,  406. 

Interstices,  100. 

Intextine,  428,  ». 

Intine  (intus,  within),  428. 

Intramolecular  respiration,  370. 

Intussusception  theory  regarding  mode 
of  growth  of  the  cell-wall  (intus  with- 
in; msceptio,  a  taking  up),  219. 

Inulin  (CeHioOs),  composition  of,  51;  oc- 
currence of,  in  plants,  358;  tests  for, 
12,  50. 

Inverted  sugar,  359. 

Iodine,  action  of  light  on  solutions  of, 
9;  action  of,  upon  callus,  93;  occur- 
rence of,  in  plants,  256;  solubility  of, 
8 ;  as  a  test  for  cellulose,  8 ;  as  a  test 
for  starch,  8. 

Ipomoea,  experiments  upon  fertilization 
of,  448. 

Iron,  necessary  for  development  of  chlo- 
rophyll granules,  254,  297 ;  occurrence 
of,  in  ash  of  plants,  247;  occurrence 
of,  in  plants,  254. 

Isodiametric  cells  (Zeros,  equal;  ««£, 
through;  n&pov,  measure),  60. 


KARYOKINESIS  (xapuov,  kernel ;  KU/«O,  I 
change),  a  term  used  to  designate  the 
series  of  changes  which  the  nucleus 
goes  through  in  cell-division. 

Kinetic  energy  (KIV«O,  I  move),  307. 

Knot,  154. 

Kraus's  process  for  extraction  of  the 
chlorophyll  pigment,  291. 

Kyanizing,  142. 

Kyanophyll  (KUOVOS,  dark  blue;  4>uAAoi<, 
'leaf),  291. 


LABURNUM,  continuity  of  protoplasm  in 

cells  of  cortex  of,  215. 
Lactuca  Scariola,  structure  of  leaves  of, 

160. 

Lacunae  (lacuna,  a  cavity),  100. 
Latex,  96. 
Latex-cells,  94. 

Latex-tubes.  See  Latex-cells. 
Laurel-camphor  (C10H160),  363. 
Layering,  444. 

Lead,  occurrence  of,  in  plants,  256. 
Leaf-trace,  131,  n. 
Leaves,  absorption  of  ammonia  by,  332, 

341 ;  absorption  of  aqueous  vapor  by, 

283;  adaptations  of,  to  climate,  280; 


490 


GLOSSARIAL   INDEX. 


alterations  in  the  color  of,  when  ex- 
posed to  bright  light,  296;  ash-con- 
stituents of  autumn  and  spring,  com- 
pared, 281;  autumnal  colors  of,  297; 
buds  on,  162 ;  chlorophyll  in  evergreen, 
298;  development  of,  155;  epidermis 
of,  161;  exogenous  structures,  155; 
fall  of,  162;  nbro-vascular  bundles 
in,  156;  glands  of,  161;  growth  of, 
156:  midrib  of,  157;  of  mosses,  164; 
of  submerged  phsenogams,  161;  pa- 
renchyma of,  158;  quality  of  light 
which  penetrates,  309 ;  relation  of  age 
of,  to  transpiration,  279;  roots  pro- 
duced from,  162;  sensitiveness  of,  419; 
transpiration  from  opposite  sides  of, 
274. 

Legumin,  363 ;  compared  with  asparagin, 
365. 

Lenticels  (lenticula,  a  freckle),  151. 

Leucites.     See  Leucoplastids. 

Leucoplastids  (\tvn6t,  white;  irAeUnrw, 
I  form),  41,  43,  287 ;  detection  of,  44. 

Lianes,  138. 

Liber-fibres.     See  Bast-fibres. 

Libriform  fibres,  80,  143. 

Lichenin  (C9H10O,),  358. 

Life  of  the  plant,  forms  of  the,  470. 

Light,  amplitude  of  -waves  of,  306 ;  classi- 
fication of  rays  of,  308;  depth  to 
which  green  tissues  are  penetrated 
by,  309;  effect  of  absence  of,  upon 
plants,  388;  effect  of,  upon  the  move- 
ments of  twining-plants,  407;  effect 
of,  upon  opening  and  closing  of  sto- 
mata,  270;  effect  of,  upon  protoplas- 
mic movements,  206;  effect  of,  upon 
transpiration,  277;  effect  of  too  in- 
tense, upon  plants,  473;  influence  of, 
upon  germination,  466;  influence  of, 
upon  respiration,  369;  influence  of, 
upon  the  structure  of  leaves,  160; 
intensity  of,  306 ;  length  of  waves  of, 

306,  n.;    nature   of,  306;    quality   of 
the,  penetrating  leaves,  309 ;  relations 
of  growth  to,  387,  392;  relations  of  the 
various  kinds  of,  to  assimilation,  305, 

307,  309,  310,  312,  316;    use  of,  in 
microscope  work,  2. 

Lightning,  effect  of,  upon  trees,  477. 
Lignification  (lignum,   wood;  fdcio,    I 

make),  34,  36/62. 
Lignin,  composition  of,  36;  solubility  of, 

36,  n.,  37 ;  tests  for,  10,  11,  13,  14, 

37. 

Lignire"ose,  37,  n. 
Lignone,  36,  n. 


Lignose,  36,  n. 

Ligules  (ligula,  a  little  tongue),  arrange- 
ment of  fibro-vascular  bundles  in, 
158. 

Lithium  used  in  the  determination  of  the 
rate  of  transfer  of  water  through  th« 
plant,  260. 

Lithocysts  (Aiflos,  a  stone;  Kv<rnt,  blad- 
der)! See  Crystal-cells. 

Living  parts  of  a  plant,  195. 

Locomotion,  397. 

Luminous  rays  of  the  spectrum,  308. 

Lycopodiacese,  stems  of,  154. 

Lysigenic  development  (A0<m,  a  parting ; 
ytwdu,  1  produce),  99,  ». 


MACERATION,  7,  12,  14,  77,  n.,  80. 

Macrocytis  pyrifera,  size  of,  188. 

Macrospore,  443,  n. 

Magenta,  19. 

Magnesium,  occurrence  of,  in  plant-ash, 
247;  office  of,  in  the  plant,  253. 

Malic  acid  (CiHoOg),  occurrence  of,  in 
plants,  360. 

Maltin,  468. 

Malting,  467. 

Manganese,  occurrence  of,  in  plants,  256. 
j    Manures,  334. 

Markings,  annular,  30,  85;  discoid,  30, 
82;  of  the  cell-wall,  29;  reticulated, 
30,  85;  scalariform,  84;  spiral,  30,  84. 

Maskenlack,  24. 

'  Measurement,  of  the  amount  of  assimi- 
lation, 312;  of  growth,  383;  of  micro- 
scopic objects,  3 ;  of  transpiration,  271 ; 
unit  of,  in  microscope  work,  4. 

Mechanical  elements,  distribution  of,  in 
dicotyledons,  193;  distribution  of,  in 
monocotyledons,  191. 

Mechanical  injuries,  effect  of,  upon 
plants,  476. 

Mechanical  irritation,  effect  of,  upon 
protoplasmic  movements.  208;  effect 
of,  upon  transpiration,  278. 

Mechanics  of  tissues,  188. 

Media,  for  examination  of  microscopic 
objects,  4  ;  mounting  or  preservative, 
20. 

Medullary  rays  (medulla,  the  pith),  61, 
114,  124. 

Medullary  sheath,  the  primary  xylem 
bundles  projecting  into  the  pith  from 
the  cambium-ring. 

Member,  a  term  employed  to  designate 
any  part  of  a  plant  when  it  is  treated 
with  reference  to  position  and  atruc- 


GLOSSAEIAL   INDEX. 


491 


ture  but  not  with  reference  to  func- 
tion. 

Membranogenic  substances  (membrana, 
a  membrane ;  yivfiv,  to  be  born),  227,  n. 

Mercuric  chloride  (HgCU),  13;  solution 
of,  for  treatment  of  protein  granules, 
45. 

Mercury,  occurrence  of,  in  plants,  256. 

Me'rismatic  (meristematic )  tissue.  See 
Meristem. 

Meristem  (fiepwrrw,  divisible),  59,  105. 

Mesophyll  (jxe<ro«,  middle;  <f>v\\ov,  a 
leaf),  the  fundamental  tissue  of  the 
leaf. 

Mestom,  191. 

Metacellulose,  35,  n. 

Metals  found  in  plants,  247,  255. 

Metaplasm  (^eri,  in  the  midst  of ;  wAao-^a, 
that  which  is  formed),  the  name  given 
by  Haustein  to  the  granular  substances 
mingled  with  protoplasm. 

Methyl-green,  19,  380. 

Metastasis  (pcroffraroi  a  removing). 
See  Transmutation. 

Methyl-violet  "  BBBBBB,"  19. 

MicefhE,  212,  257,  393;  attractions  of, 
212,  218. 

Micrometer,  3. 

Micro-millimeter,  4. 

Micropyle  (fxncpov,  small;  m»A>7,  orifice), 
433. 

Microscope,  1. 

Microsomata  (fu*p<k,  small ;  wno.,  body), 
211. 

Micro^pectroscope,  292. 

Microspore,  443,  n. 

Microtome,  use  of  the,  in  section-cut- 
ting, 3. 

Mikroskopirlack,  24. 

Milk-sacs,  99. 

Millon's  reagent  (Acid  Nitrate  of  Mer- 
cury), 13,  28,  33. 

Mimosa  pudica,  420. 

Mineralization,  34,  39. 

Mirror  of  microscope,  2. 

Modifications  of  the  cell-wall,  34. 

Moisture,  effect  of  amount  of,  in  the  air 
upon  transpiration,  276;  effect  of 
forests  upon  the  amount  of,  in  the 
air,  281;  effect  of.  upon  the  direction 
of  growth,  393;  exhalation  of,  by 
desert  plants,  276;  relations  of  proto- 
plasm to,  209;  relations  of  soils  to, 
239.  See  also  Water. 

Molecule,  212,  n. 

Monocotyledons,  distribution  of  mechan- 
ical elements  in,  191;  secondary  struc- 


ture of  stems  of,  135;  stems  of,  129; 
tvpes  of  stems  of,  133. 

Morphia  (CnH»NOi  +  H20),  327,  365, 
476. 

Mosses,  absorbing  organs  in,  117;  aid 
the  soil  in  retention  of  water,  282; 
leaves  of,  164;  reproduction  in,  441, ».; 
stems  of,  154. 

Mother  cells,  of  pollen,  171,  379;  of  sto- 
mata,  72,  376. 

Mounting-media,  20. 

Movements,  cause  of  autonomic,  nu 
fully  known,  414;  due  to  changes  in 
structure  during  ripening  of  fruits, 
400;  hygroscopic,  399;  of  ciliated 
structures,  398;  of  Desmids,  398;  of 
Diatoms,  398;  of  leaves,  419 ;  of  proto- 
plasm, 199r  398;  of  seedlings,  403;  of 
the  Telegraph  plant,  413;  of  tendrils, 
409,  417;  of  twining  plants,  405;  of 
young  parts  of  mature  plants,  405; 
revolving,  400;  sleep,  409;  sleep,  of 
cotyledons,  411;  sleep,  of  floral  or- 
gans, 412;  spontaneous,  413;  utility 
of  sleep,  411. 

Mucedin,  364. 

Mucilage,  conversion  of  the  cell-wall 
into,  34;  in  the  cell-sap,  51;  solubility 
of  vegetable,  33. 

Mucilage-cells,  99. 

Mucilaginous  modification  of  paren- 
chyma cells,  63. 

Mucus,  220. 

Mulder's  hypothesis  concerning  the  ort- 
gin  of  albuminoids,  326,  n. 

Multiple  epidermis.  67. 

Myxomycetes,  196,  414. 

NAEGKLI'S  HYPOTHESIS  concerning  the 
structure  of  organized  bodies,  212. 

Nascent  tissue  (nasceiw,  arising).  See 
Meristem. 

Natural  grafts,  152. 

Nectar,  451;  protection  of,  from  the 
visits  of  unwelcome  insects,  455 ;  secre- 
tion of,  452;  specific  gravity  of,  452. 

Nectar-glands,  161,  451. 

Nectar  guides  or  spots,  453. 

Nectaries,  452. 

Negative  geotropism,  392. 

Negative  heliotropism,  393. 

Nepenthes,  349. 

Nervation  of  seed-coats,  180. 

Nerves  of  leaves,  156. 

Nickel,  occurrence  of,  in  plants,  256. 

Niggl's  test  for  lignin,  13. 


492 


GLOSSABJAL   INDEX. 


Nigrosin,  19,  380. 

Nitrates,  as  a  source  of  plant-food,  335; 
test  for,  326,  n. 

Nitric  acid  (HNO»),  13;  as  a  source  of 
plant-food,  335. 

Nitrogen,  amount  of,  in  plants,  327; 
amount  of,  in  rain-water,  331 ;  appro- 
priation of,  by  plants,  325,  330 ;  com- 
parative needs  of  wild  and  cultivated 
plants  for,  334 ;  compounds  of,  in  the 
atmosphere,  331:  in  coloring-matters 
of  leaves,  292;  in  the  soil,  333;  mode 
of  formation  of  atmospheric  com- 
pounds of,  332 ;  sources  of,  for  plants, 
327. 

Non-sexual  reproduction,  426,  444. 

Nucellus,  175,  182,  433. 

Nuclear  disc,  376. 

Nuclear  spindle,  376. 

Nuclein,  375,  376,  378. 

Nucleus,  25,  n.,  28,  199,  220,  374;  be- 
havior of  the,  with  reagents,  375;  dem- 
onstration of  changes  in  the,  in  the 
development  of  pollen-grains,  380; 
structure  of  the,  375. 

Nucleus  cellulas,  27,  n.     See  Nucleus. 

Nucleus  of  a  starch-granule.    See  Hilum. 

Nucleus  of  the  ovule.     See  Nucellus. 

Nucleolus,  28,  375. 

Nutation  (nutatio,  a  nodding),  400. 

Nutrition,  355. 

Nyctitropic  movements  (™'f  [gen. 
night;  rpoiros,  a  turn),  409. 


OAKS,  histological  classification  of, 
143,  n. 

Objectives,  2. 

Odors,  of  flowers,  454;  of  wood,  142. 

Oil  in  seeds,  361. 

Oil  of  cloves.  3,  23. 

Oleic  acid  (C.jH^O,),  360. 

Olein  (C^H^O,,),  360. 

Olive-oil,  use  of,  in  experiments  on  pro- 
toplasmic movements,  211. 

OSphytes,  reproduction  in,  440,  ». 

Oosphere  (<*>",  an  egg;  •r^alpo,  a  sphere), 
435,  440,  n.,  441,  n. 

Oospore  (Mv,  an  egg;  <nn>po«,  seed),  436, 
440,  n. 

Open  bundles,  104. 

Opening  and  closing  of  flowers,  412. 

Orange  "R,"  19. 

Orchids,  trachelds  in  roots  of,  109. 

Organ,  102,  186;  rank  of  an,  186,  n. 

Organic  acids,  effect  of,  upon  turges- 
cence,  414. 


Organic  matter,  appropriation  of,  by 
the  plant,  337;  changes  of,  in  the 
plant,  354. 

Organic  products,  classification  of, 
357. 

Osmic  acid  (perosmic  acid)  (OsO4),  14, 
46. 

Osmometer  (u»7/xd«,  impulse;  ^trpov,  mea- 
sure), 224. 

Osmosis  (uo>i6f,  impulse),  221,  224. 

Osmotic  equivalent,  225. 

Osmundacea?,  stems  of,  154. 

Ovary  (ovum,  an  egg),  arrangement  of 
fibro-vascular  bundles  in  an  inferior, 
174;  arrangement  of  fibro-vascular 
bundles  in  a  superior,  173;  structure 
of  the,  172;  varieties  of  conductive 
placentae  in  an,  432. 

Ovules,  changes  in  the  fertilization  of, 
435;  development  of,  433;  formation 
of,  175;  ripening  of,  178;  structure  of 
the,  in  angiosperms,  432 ;  structure  of 
the,  in  gymnospenns,  438. 

Ozone,  304. 

Oxalates,  test  for,  9,  54. 

Oxalic  acid  (CjH.O*),  360. 

Oxidation,  355. 

Oxygen,  an  agent  in  the  disintegration 
of  rocks,  237;  amount  of,  absorbed 
during  respiration,  368;  amount  of, 
evolved  in  assimilation,  319;  necessary 
for  germination,  464;  necessary  for 
protoplasmic  movements,  210;  of  air 
ample  for  respiration,  368;  relations 
of  growth  to,  388;  required  bv  roots, 
245. 


PALISADK-CEI.LS,  61,  159. 

Palmate  venation  in  leaves  (pnlmatw, 
bearing  the  mark  of  a  hand),  157. 

Palmatin  (CnHagOr,),  360. 

Palmitic  acid  (CI9HWO>),  360. 

Palms,  fibro-vascular  bundles  in,  130, 
131. 

Paper-pulp,  manufacture  of,  146. 

Paracellulose,  35. 

Paraffin,  use  of,  in  section-cutting,  3. 

Parallel  venation  in  leaves,  156. 

Parasites  (»ropo<riTo?,  one  who  lives  at 
another's  expense),  289,  338;  chloro- 
phyll lacking  in  certain.  294;  food  of, 
338;  roots  of,  116;  union  between,  and 
their  hosts,  153,  338. 

Parchment  paper,  32,  n.  use  of,  in 
making  osmometer.  224. 

Parenchyma  (wa^tyx***- 1  p°ur  >n  beside). 


GLOSSABIAL  INDEX. 


493 


57,   60 ;    elements  of,   60 ;   forms    of 

celj?  of,  61;  in  the  fascicular  system, 

102;  of  the  flower,  170;  of  the  fruit, 

176;  of  the  leaf,  158;  of  the  petiole, 

160;  of  the  stem,  119,  124;  sclerotic, 

62;  thin-walled,  62. 
Parthenogenesis     (*ap9ivtn,    a    virgin; 

yivwi,  production),  446. 
Path  of  water  through  the  plant,  259. 
Peaty  soils,  239. 
Pectin  bodies,  358. 
Pectose,  34,  n.,  358. 
Pellicle-membrane,  227. 
Perennials,  storing  of  assimilated  matter 

in,  373. 
Periblem   Uepi/JAiipa,  a  covering),  105, 

118,  155. 

Pericambium,  113. 
Periclinal  planes  (irepi,  around ;  /cAiVw,  I 

incline),  382. 
Periderm  (*tpi,    around;    *«>Ma,  skin), 

75. 

Periodic  movements  of  organs,  409. 
Peripheral  tissue  of  rootlets,  108. 
Perisperm    (**&,    around;    <rw«p/x«,  the 

seed),  437. 
Peristome,  441,  n. 
Perosmic  acid.     See  Osmic  Acid. 
Petiole  (pttiolui,  a  little   foot),  paren- 
chyma of  the,   160;   sensitiveness  of 

the,  419. 
Pfeffer's  experiments  with  artificial  cells, 

226. 
Phelloderm  («J>e\Ao«(  cork;  Sippa,  skin), 

75,  148,  n. 

Phellogen  (<£<AA<k,  cork;  ytwaa,  I  pro- 
duce), 74,  148. 
Phenol.    See  Carbolic  Acid. 
Phloem  (4.AOKK,  inner  bark),  104. 
Phloroglucin  (C»H«O3),  use  of,  as  a  test 

for  lignin,  14.  37. 
Phosphorus,  occurrence  of,  in  plant-ash, 

247;  office  of,  in  the  plant,  258. 
Phosphorescence,  370. 
Phototonus,  423. 
Phycocyanine  (*0«o«,  sea-weed;  *V<LV<K, 

dark  blue),  295. 
Phycoerythrine    (4.0«K,   sea-weed;  ipv- 

6p6s,  red),  295. 
Phycopha'ine   (*v««,    sea-weed;    *«««, 

brown),  295. 
Phycoxanthine  (*C*o«,  sea-weed ;  fai-Ws, 

yellow),  295. 
Phyllocladia     fovAAoK,      leaf;      icXoio?, 

a  young  branch),  280. 
Phyllocyanin  (<frvAAoK,  leaf;  Kv<m>*,dark 

bine),  290. 


Phyllodia  (^uAAui^s,  like  leaves),  280. 

Phyllophore  (<t>v\\ov,  leaf ;  <t>op^,  I  bear), 
132. 

Phylloxanthin  (<i>v\\ov,  leaf;  fa»0oS)  yel- 
low), 290. 

Physical  properties  of  soils,  239. 

Picric  acid  (C«H3[N02]3OH),  18. 

Piliferous  layer  (pilus,  hair;  fero,  I 
bear),  108. 

Pinguicula,  345. 

Pinnate  venation  in  leaves  (pinnatus, 
feathered),  157. 

Pistils,  changes  of,  in  ripening,  176; 
fibro-vascular  bundles  in,  173;  sensi- 
tiveness of,  424;  structure  of  angic- 
spermous,  427. 

Pith,  124;  solubility  of,  34,  n. 

Planes  of  the  cell-wall  at  the  point  of 
growth,  381. 

Plasmolysis  ()rAa<r/bia,  what  has  been 
formed :  Avais,  a  loosing),  390,  n. 

Plasmolytic  agent*,  27,  n.,  390;  effect  of, 
upon  protoplasm,  210. 

Plastids  (irAa<ro-u>,  I  form),  40,  287. 

Pleon  (irMor,  full),  212. 

Plerom  (irA^pw^o,  that  which  fills),  105, 
118. 

Poisons,  effects  of,  upon  plants,  473. 

Polarizing  apparatus,  4. 

Pollen  (pollen,  fine  flour),  amount  of, 
produced  by  flowers,  432;  bursting  of 
grains  of,  in  water,  429 ;  contents  of 
grains  of,  428;  development  of,  171, 
379;  effect  of  sugar  solutions  on 
grains  of,  429;  of  angios perms,  427; 
of  gymnosperms,  437;  structure  of, 
428;  "vitality  of,  431. 

Pollen-tube,  emission  of  the,  430;  time 
required  for  descent  of  the,  431. 

Pollinia,  427. 

Pollinic  chamber,  438. 

Polyembryony  (iroAw,  many; 
embryo),  446. 

Ponceau,  19. 

Poplar,  glands  on  leaf  of  the,  161. 

Potash  (KOH),  diffusion  of,  222;  use  of, 
as  a  reagent,  6 ;  use  of,  in  examina- 
tion of  chloroplastids,  42;  use  of,  in 
section-cutting,  3,  n. 

Potassic  acetate  (KC2H,02),  use  of,  M  a 
mounting-medium,  21. 

Potassic  bichromate  (KjCrjOr),  I*- 

Potassic  chlorate  (KC103),  14- 

Potassic  ferrocvanide  (K4Fe[CN]e),  use 
of,  in  making  precipitation-mem- 
branes,  225. 

Potassic  nitrate  (KNO.,),  15,  390,  n. 


4D4 


GLOSSAKIAL    INDEX. 


Potassium,  occurrence  of,  in  plants,  247; 
office  of,  in  the  plant,  252. 

Potential  energy,  307. 

Precipitation-membrane,  225. 

Preparation  of  specimens,  21. 

Preservation  of  wood,  142. 

Pressure,  effect  of  atmospheric,  upon 
germination,  369,  464;  effect  of  atmos- 
pheric, upon  growth,  389;  effect  of, 
upon  movements  of  protoplasm,  208 ; 
growth  retarded  by  external,  395 ;  of 
sap  in  the  stem,  264. 

Prickles,  69. 

Primary  cortex,  119. 

Primary  membrane,  36. 

Primary  structure,  105;  of  the  root,  106; 
of  the  stem,  119. 

Primine  ( primus,  first),  178. 

Primordial  tissues,  58. 

Primordial  utricle,  27,  «.,  220. 

Procambium,  104. 

Prosenchyma  (irp<5«,  near;  <"-yxv>*a>  an  in- 
fusion)', characteristics  of,  58,  76;  in 
the  fascicular  system,  102. 

Proteids,28,  326,  n.;  formation  of,  in  the 
plant,  335. 

Protein  basis,  46. 

Protein  granules,  44;  classification  of, 
in  seeds,  182. 

Prothalli,  442,  n. 

Protogenic  development  (irpuroi,  first; 
ytwdut,  I  produce),  99,  n. 

Protophytes,  439,  n. 

Protoplasm  (irpim>?,  first ;  irAa^a,  what 
has  been  formed),  amoeboid  movement 
of,  201;  appearance  of,  26;  chemical 
properties  of,  197;  circulation  of,  199, 
398;  composition  of,  28, 197 ;  continuity 
of,  in  cells,  214;  discrimination  between 
living  and  dead,  10,  470,  n. ;  effect  of 
mechanical  irritation  upon,  208;  ex- 
amination of,  196,  198,  202;  film  of, 
envelops  many  crystals,  54;  historical 
note  regarding,  219;  in  young  cells, 
198;  movements  of  naked,  200,  201, 
397 ;  movements  of,  dependent  on  the 
absorption  of  moisture,  212,  n.;  nitro- 
gen in,  325;  passage  of,  through  imper- 
forate  cell-walls.  217;  physical  proper- 
ties of,  197 ;  rate  of  movements  of, 
200;  reaction  of,  198;  relations  of,  to 
anaesthetics,  211 ;  relations  of,  to  elec- 
tricity, 207;  relations  of,  to  gravita- 
tion/209;  relations  of,  to  light,  206; 
relations  of,  to  moisture,  209;  relations 
of,  to  plasmolytic  agents,  210;  rela- 
tions of,  to  temperature,  201;  rela- 


tions of,  to  various  gases,  210;  rela- 
tions of  the  cell-wall  to,  218;  rotation 
of,  200;  structure  of,  211;  tesfs  for, 
28;  vitality  of,  in  seeds  and  spores, 
205;  water  contained  in,  198,  257. 

Pulsation  of  vacuoles,  397. 

Pulvini  (pulvinus,  a  cushion),  160,  404, 
410;  continuity  of  protoplasm  in  the 
cells  of,  215;  in  the  Sensitive  plant, 
420 ;  in  the  Telegraph  plant,  414. 

Putrefaction,  results  of,  333. 

Pyreuoids  (nvpjv,  a  kernel;  eZSo*,  form), 
287,  n. 


QUEKCITKIN  (C»H,o07),  362. 

Quinia  (C^NaO,  +  H,0),  327,  365. 


RADIAL  BUNDLE,  104. 

Radial  planes,  382. 

Radicle,  118;  movements  of  the,  403; 
structure  of,  106. 

Kain-fall,  effect  of  forests  upon  the, 
282. 

Rain-water,  gases  in,  300,  n.;  nitrogen 
compounds  in,  331. 

Ranvier's  picrocarmin,  17. 

Raphides  (p**'«  [gen.  pa#«o«],  a  needle), 
52. 

Razor,  use  of  the,  in  section-cutting,  3. 

Reagents,  4;  employment  of,  6. 

Receptacles  for  secretions,  97,  110. 

Recording  auxanometer,  383. 

Red  anilin,  19. 

Rejuvenescence  (re,  again ;  juvenetco,  1 
become  young),  the  formation  of  » 
single  new  cell  from  the  protoplasm 
of  a  cell  already  in  existence. 

Repair  of  waste,  355. 

Reproduction,  425;  by  budding,  444; 
contrast  between  methods  of,  as  re- 
gards results,  443;  in  cryptogams, 
439,  n. ;  methods  of,  426. 

Reserve  protein  matters,  44. 

Resin-cells,  97. 

Resins,  98,  363;  detection  of,  12. 

Respiration,  355, 356,  367  ;  accompanied 
by  evolution  of  heat,  370;  contrasted 
with  assimilation,  356;  early  history 
of,  367;  influence  of  light  and  temper- 
ature upon,  369 ;  intramolecular,  370. 

Resting  state,  369,  389,  459. 

Resurrection  plant,  399. 

Retention  of  moisture  by  soils,  239. 

Reticulated  markings,  30,  85. 

Reticulated  venation  in  leaves,  156- 


GLOSSARIAL   INDEX. 


495 


Revolving  nutation,  400. 

Rhizogenic  cells  (P^O,  a  root;  y«wdo>,  I 

produce),  115,  «. 
Rhizoids  (?<£<»,  a  root ;  «M<x,  like),  777, 

230. 
Rhizomes  (pifw/no,  that  which  has  taken 

root),  structure  of,  153. 
Rhodospermin  (poSov,  rose ;  <nrep^a,  seed,) 

295. 

Ripening  of  fruits  and  seeds,  460. 
Rocks,  disintegration  of,  237. 
Root-cap,  106,  107. 

Root-hairs,  108;  corrosive  action  of, 
246;  distortion  of,  231;  increase  the 
absorbing  surface  of  a  root,  231;  meth- 
od of  obtaining  for  study,  109 ;  num- 
ber of,  on  different  plants,  231 ;  office 
of,  in  absorption,  231;  size  of,  231; 
walls  of,  108, 109. 

Roots,  absorption  by,  230,  244;  amount 
of  branching  of,  232 ;  central  cylinder 
of,  110;  colors  of,  116;  cortex  of,  110; 
crown,  153;  depth  to  which  branching 
of,  occurs,  233;  extent  of,  232,  235; 
formation  of,  107,  155;  from  leaves, 
162;  growth  of,  107;  influence  of  the 
soil  upon,  234;  of  cryptogams,  116;  of 
orchids,  109 ;  oxygen  needed  by,  245 ; 
parasitic,  116;  piliferous  layer  of,  108; 
primary  structure  of,  106;  secondary 
structure  of,  112;  types  of  branching 
of,  115,  n. 
Roridula,  345. 
Rose  of  Jericho,  400. 
Rosolic  acid.     See  Corallin. 
Rotation  of  protoplasm,  200. 
Rubidium,  occurrence  of,  in  plants,  256. 
Rudimentary  branches,  153. 
Russia  matting,  147. 
Russow's  potash-alcohol,  7. 


SAFRANIN  (C^N,),  19,  380. 

Salicin  (C,,HI807),  362. 

Saline  matters,  absorption  of,  by  roots, 
244. 

Sandy  soil,  238. 

Sap,  amount  of,  in  plants,  265;  flow  of, 
from  plants,  264;  pressure  of,  264, 
265. 

Saprophytes  (<r<nrpds,  putrid;  fa™,  a 
plant)',  289,  294,  357. 

Sap-wood.  141. 

Sarcode,  220. 

Sarracenia,  347 

Scalariform  markings  (scalaria,  a  lad- 
der; forma,  form),  30,  84. 


Scales,  69. 

Schizogenic     development     (wfr,     I 

cleave;  yevxdu,  I  produce),  99,  n. 
Schleim,  220. 

Schulze's  macerating  liquid,  14,  38,  39. 
Schulze's  reagent,  9,  33,  76,  77,  n. 
Schweizer's  reagent,  12,  15,  32. 
Scion,  152,  444. 
Sclerenchyma  (oxAtjpds,  hard;  iyxvpa.,  an 

infusion),  87. 
Sclerotic  parenchyma  (crxAijpo?,   hard), 

62. 

Secondary  liber,  113. 
Secondary  structure,  105;  of  roots,  112; 

of  stems,  135. 
Secondary  wood,  113. 
Secretions,  of  nectar,  451;   receptacles 

for,  97,  110 ;  stigmatic,  427. 
Section-cutting,  3. 
Secundine  (secundus,  second),  178. 
Seeds,  albuminous  and   exalbuminous, 
181 ;  arrested  activity  of,  459 ;  changes 
during  the  ripening  of,  460;  dissemina- 
tion of,  400,  460 ;  food  in,   182,  437, 
467 ;  germination  of,  462 ;  germination 
of  oil  v  and  starchy,  compared,  368 ;  im- 
mature, 460 ;  increase  of,  in  size,  upon 
the  absorption  of  water,  463 ;  integu- 
ments  of,  178;   minute  structure  of, 
178;  protein  granules  in,  182;  ripeness 
of,  460;  vitality  of,  205,  461. 
Selenium,  occurrence  of,  in  plants,  256. 
Sensitiveness,  414 :  effect  of  anaesthetics 
upon,  424;  of  leaf-blades,  419;  of  peti- 
oles, 419;  of  roots,  415;  of  stamens, 
423;  of  stems  and  branches,  417;  of 
styles,  424. 

Sensitive  plant,  420,  424. 
Sensitive  tissues,  415. 
Shell-lac,  24. 

Sieve-cells,  91, 103, 112;  contents  of,  94; 
development  of,  122;  of  cryptogams, 
94;  of  gymnosperms,  94;  size  of,  92. 
Sieve-plates,  91,  92. 
Sieve-pores,  91,  93. 
Sieve-tubes.    See  Sieve-cells. 
Silica  (Si02),  deposits  of,  in  plants,  39. 
Silicium,  office  of,  in  the  plant,  255. 
Silphium    laciniatum,    arrangement    of 

parenchyma  in  the  leaf  of,  160. 
Silver,  occurrence  of,  in  plants,  256. 
Simple  hairs.  68. 
Simple  microscope,  1. 
Simple  pistils,  173. 

Sleep-movements,  409;  of  cotyledons, 
411;  of  floral  organs,  412;  utility  of, 
411. 


496 


GLOSSABIAL   INDEX. 


Slides  (slips),  2. 

Sodic  chloride  (NaCl),  15;  diffusion  of, 

222,  223. 

Sodic  hydrate  (NaOH),   use  of,   as  a 
reagent,  7;  use  of,  in  the  manufacture 
of  paper-pulp,  147. 
Sodic  hypochlorite  (NaCIO),  11. 
Sodium,  can  partly  replace  potassium  in 
plants,  255;  occurrence  of,  in  plants, 
247. 

Soft  bast,  the  unlignitied  cells  of  the 
liber  portion  of  a  fibro- vascular  bundle. 
Soils,  absorption  of  heat  by,  245;  ab- 
sorption and  retention  of  moisture  by, 
239,  282;  chemical  absorption  by,  243; 
classification  of,  238;  condensation  of 
gases  by,  244;  effect  of  transpiration 
upon,  283;  evaporation  from,  241,  282; 
filtration  through,  242;  formation  of, 
237;  influence  of,  upon  roots,  234;  in- 
fluence of,  upon  transpiration,  276; 
mechanical  ingredients  of,  239;  nitro- 
gen available  to  plants  in,  333 ;  physi- 
cal properties  of,  239;  root-absorption 
of  saline  matters  from,  244;  tempera- 
ture of,  245;  transportation  of,  by 
water,  238. 

Solatium     Pseudocapsicum,      coloring- 
matters  in  berries  of,  177. 
Solid  yellow,  19. 

Sources  of  nitrogen  for  the  plant,  327. 
Specific  gravity  of  wood,  144. 
Spectrum,  classification  of  the  rays  of 
the,  308 :  effect  of  the  r&ys  of  the,  upon 
protoplasmic  movement,  206;  effect  of 
the  rays  of  the,  upon  transpiration, 
278;  of  chlorophyll,  292,  313. 
Spermoderm  (aire^a,  seed ;  ««>>to,  skin), 

178. 
Sphieraphides    (<r<j><ilpa.    sphere;    patfu?, 

needle),  53. 
Sphere- crystals,  53. 
Spines,  69. 

Spiral  markings,  30,  84. 
Spongiole  (ipongiola,  a  little  sponge), 

230. 

Spongy  cortex,  120. 
Spongy  parenchyma,  61. 
Sports.  444. 
Spring  wood,  138,  396;  transfer  of  water 

through,  258. 

Staining  agents,  15;  effect  of,  upon  pro- 
toplasm, 210. 
Stamens  (stamen,  a  thread),  development 

of,  171;  sensitiveness  of,  423. 
Starch,  amount  of,  in  plants,  357;  ap- 
pearance   of,    when    examined    with 


polarized  light,  50;  conversion  of.  into 
sugar,  357,  467;  composition  of,  50; 
first   visible   product   of  assimilation, 
321;  in  latex,  96;  in  seeds,  182;  pres- 
ence of,  in  chloroplastids,  42;  produc- 
tion of,  in  a  plant  dependent  on  potas- 
sium, 252;  solubility  of,  49;  structure 
of,  47;  tests  for,  8,  50. 
Starch  cellulose,  50. 
Starch  generators.     See  Leucoplastids. 
Steam,  action  of,  on  chlorophyll  gran- 
ules, 290,  475,  n. 
Stearic  acid  (C,gHM0,),  360. 
Stearin  (CjrHnoO,,),  360. 
Stellate  hairs  (stella,  a  star),  69. 
Stellate  scales,  69. 

Stems,  118;  bleeding  of,  264;  course  of 
fibro-vascular  bundles  in,  125;  cortex 
of,  119;  development  of,  124;  dicoty- 
ledonous (exogenous),  129, 136 ;  epider- 
mis of,  119;  fibro-vascular  bundles  of, 
120;    injuries    of,    149;    monocotyle- 
donous   (endogenous),  129,  133,  i35; 
of  mosses,   154;    of  vascular  crypto- 
gams, 154;  pitli  of,    124;  pressure  of 
sap  in,  264;  primary  structure  of,  119; 
secondary  structure  of,  135;  sensitive- 
ness of,  417 ;  transfer  of  water  through, 
258 ;  wilting  of  cut,  263. 
Stereom  (ropw,  firm),  191. 
Stigma  (oriyno,  a  mark    made    by    a 
pointed  instrument),  427 ;  character  of 
the  cells  of  the.  172;  extent  of  surface 
of  the,  427,  430. 
Stigmatic  secretion,  427. 
Stock,  152. 

Stomata  (vrona,  the  month),  70,  268;  de- 
velopment of,  72.  376 ;  guardian  cells 
of,  70,  269;  mechanism  of,  269 ;  occur- 
rence of,  70,  n.,  71,  ».,  72;  passage  of 
gases  through,    303 ;   relations  of,  to 
exter  al  influences,  270;  size  of,  71. 
Stratification,  30. 
Striation,  30. 

Stroma  (<TrpS>na.,  a  bed),  198. 
Strontium,  occurrence  of,  in  plants.  256. 
Structural  characters  of  wood,  146,  n. 
Strychnia  (CsiH«N,O,).  365. 
Style  (stilus,  a  style),  427;  character  of 
the  cells  of  the,  172;  conductive  tissue 
of,  431 ;  sensitiveness  of,  424. 
Suberification    (suber,    cork;    facto,    I 

make),  34.  38. 

Suberin,  38;  tests  for,  7,  14,  39.  • 

Submerged  phwnogams.  leaves  of,  161. 
Substitute  fibres,  80. 
Sugar,  diffusion  of,  222 ;  effect  of  a  solu- 


GLOSSARIAL   INDEX. 


497 


tion  of,  on  pollen-grains,  429;  in  the 
cell-sap,  52;  use  of,  as  a  reagent,  15, 
199. 

Sugar  group  of  non-nitrogenous  prod- 
ucts, 358. 

Sulphur,  appropriation  of,  by  the  plant, 
255,  284,  336;  in  the  ash  of  plants, 
247. 

Sulphuric  acid  (HaSO«),  effect  of,  upon 
cellulose,  15,  31;  effect  of,  upon  cuti- 
nized  membranes,  39;  use  of,  as  a  sol- 
vent for  callus,  93. 

Sulphurous  acid  (S02),  effects  of,  upon 
leaves,  474. 

Superior  ovaries,  arrangement  of  the 
fibro-vascular  bundles  in,  173. 

Suspensor,  436. 

Synergidse  (<rv«pyds,  working  together), 
435. 

Syntagma  (owrayfta,  that  which  is  put 
together  in  order),  218,  n. 

Synthesis  of  albuminous  matters  in  the 
plant,  335. 

Systems,  102. 


TABASHEKR,  39,  n. 

Tagma  (ray^a,  a  company),  213,  n. 

Tannate  of  gelatin  used  in  the  formation 
of  Traube's  cell,  226. 

Tannin  (C14H,0O»),  diffusion  of,  222;  in 
pulvinus  of  Mimosa,  361,  420;  occur- 
rence of,  in  plants,  361 ;  tests  for,  12, 
14. 

Tapetum  (tapete,  a  carpet),  171,  n. 

Tartaric  acid  (C«H.Qi),  360. 

Teasel.     See  Dipsacus. 

Tegmen  (tegmen,  a  covering),  178. 

Telegraph  plant,  413. 

Temperature,  effect  of,  upon  absorption 
by  soils,  240;  effects  of  too  high,  upon 
plants,  470;  elevation  of,  during  intra- 
molecular respiration,  372;  influence 
of,  upon  absorption  by  roots,  245 ;  influ- 
ence of,  upon  assimilation.  306,  316; 
influence  of,  upon  respiration,  369;  in- 
fluence of,  upon  transpiration,  277 ;  of 
air  inside  a  spathe,  370;  of  pulvinus 
of  Mimosn,  421 ;  producing  rigidity 
in  Sensitive  plant,  423;  relations  of 
growth  to,  385;  relations  of  protoplasm 
to,  201 ;  relations  of  soils  to,  245 ;  rela- 
tions of,  to  germination,  464. 

Tendrils,  circumnutation  of,  409,  417. 

Tensions  of  the  cell-wall  and  tissues, 
390. 

Terpene  (C,«H18),  362. 


!    Tertiary  formations  in  the  root,  115. 

Testa  (testa,  a  shell),  178. 

Tetrad  (rerpas,  four),  171. 

Thallium,  occurrence  of,  in  plants,  256. 

Thallophytes,  164,  440. 

Tharandt  normal-culture  solution,  250. 

Thermotropic  curvatures,  394. 

Thermotropism  (Ocp^ov,  heat;  Tpdn-os,  a 
turn),  394. 

Thiersch's  borax-cannin,  17. 
i    Thiersch's  oxalic-acid  carmin,  17. 

Times  of  opening  and  closing  of  flowers, 
412. 

Tin,  occurrence  of,  in  plants,  256. 
j    Tissues,  102;  classification  of,  187;  con- 
ducting power  of  ligneous,  261;  cribri- 
form, 91;  depth  to  which  light  pene- 
trates, 309;  hardening  of,  9,  11;  rela 
tions  of  water  to,  257;  sensitive,  415; 
tension  of,  390. 
|    Titanium  occurrence  of,  in  plants,  256. 

Trabecular  ducts  (trabecula,  a  little 
beam),  86. 

Tracheae  (rpaxda.,  rough),  82,  84.  See 
also  Vessels. 

Tracheal  cells,  81. 

Tracheal  portion  of  a  fibro-vascular 
bundle,  104. 

Tracheids,  82;  in  roots  of  orchids,  109; 
in  stems,  121;  size  of,  143;  walls  of, 
j       84. 

Transfer  of  water  through  the  plant,  257 ; 
compared  with  that  through  porous 
inorganic  substances,  262,  ». ;  effect  of 
exposing  a  cut  surface  to  the  air  upon, 
263;  effect  of  motion  upon,  263;  path 
of,  259;  rate  of,  259,  261. 

Transformed  branches,  153. 

Transformed  cells,  56. 

Transmutation,  354,  355. 

Transpiration,  268;  amount  of  water 
given  off  in,  271,  275.  281;  apparatus 
for  registering,  273;  checks  upon,  280; 
compared  with  evaporation  proper, 
275;  effect  of  various  salts  upon, 
279;  effect  of  heat  upon,  277;  effect 
of  light  upon,  277 ;  effect  of  mechani- 
cal shock  upon,  278;  effect  of  moisture 
in  the  air  upon,  275;  effect  of  nature 
of  the  soil  upon,  276;  effects  of,  upon 
the  air,  281 ;  effects  of,  upon  the  plant. 
281;  effects  of,  upon  the  soil,  283; 
experiments  upon,  273;  methods  of 
measuring,  272;  relation  of  age  of 
leaves  to,  279;  relation  of,  to  absorp- 
tion, 279;  relative  amounts  of,  from 
opposite  sides  of  a  leaf,  274. 


498 


GLOSSAKIAL    INDEX. 


Transverse  planes,  382. 

Trees,  age  of,  139. 

Trichobiast  (Opi(  [gen.  TPiXos],  hair; 
flAaoro*,  shoot),  a  name  proposed  by 
Sachs  for  such  idioblasts  as  are  es- 
pecially distinguished  by  size  and 
brandling. 

Trichogyiie,  440,  n. 

Trichomes  (fl.^f,  hair),  65,  68,  230. 

Trinitrophenic  acid.     See  Picric  Acid. 

Triolein.     -See  Olein. 

Tripalmatin.    See  Palmatin. 

Tristearin.     See  Stearin. 

Trommer's  test  for  dextrin,  51. 

Trophoplast  (rp.x/,6*,  a  feeder;  n\d<rvu,  I 
fonn),  287. 

Tiillen.     See  Tyloses. 

Turgescence,  effect  of  organic  acids  upon. 
414. 

Turpentine  (C,»H,B),  use  of,  in  prepara- 
tion of  specimens  for  mounting.  23. 

Twining  plants,  405. 

Tyloses  (rv'Ao?,  a  protuberance),  87. 

Typical  cells.     See  Fundamental  Cells. 

UNORGANIZED  FERMENTS,  365. 
Utricularia,  346. 

VACCOLES,   26,  177,  200,  212.  n.,  280, 

375,  397. 

Variegated  plants,  477. 
Varieties,  447. 
Variety-hybrids,  455. 
Vascular  system.      See   Fibre-vascular 

System. 

Vasculose,  35,  n. 
Vasiform  elements  (vat,  vessel;  forma, 

form).  81. 

Vasiform  wood-cells.    See  Trachelds. 
Vegetable  acids,  360. 
Vegetable    mucus,    occurrence    of,    in 

plants,  358;  test  for,  15. 
Vegetable  parchment,  32,  n. 
Venation  of  leave*,  156. 
Vesque's  method  of  producing  crystals, 

55. 
Vessels,  55,  77,  82,  84;   classified,  60; 

size  of,  86. 
Viola  tricolor,  coloring-matters  in  flowers 

of.  170. 

Vitality  of  seeds,  205,  461. 
Vitellin,  364. 

WARDIAN  CASES,  474. 

Water,   absorbed  previous  to  metasta- 


sis, 267;  absorption  of  gases  by,  300, 
n. ;  action  of  steam  upon  chlorophyll, 
290,  475,  n. ;  an  agent  in  the  formation 
of  soils,  237 ;  amount  of,  contained  in 
plants,  236 ;  amount  of,  given  off  in 
transpiration,  271 ;  amount  of,  required 
for  germination,  462;  direction  in 
which  tissues  most  readily  conduct, 
262,  ».;  effect  of  absorption  of,  upon 
seeds,  463  ;  effect  of,  upon  protoplas- 
mic movements,  20!) ;  effect  of,  upon 
opening  and  closing  of  stomata,  270; 
equilibrium  of,  in  the  plant,  258;  ex- 
udation of,  from  uninjured  parts  of 
plants,  267,  method  of  determining 
amount  of,  in  dry  wood,  261 ;  rate  of 
ascent  of,  in  stems,  261,  263;  relations 
of,  to  tissues,  257 ;  relative  amount  of 
.space  occupied  by,  in  fresh  wood,  261; 
transfer  of,  in  plants,  257,  269;  trans- 
port of  <oils  by,  238;  use  of,  as  a 
medium,  5;  use  of,  as  a  mounting- 
medium,  21.  See  also  Moisture. 

Water-culture,  248:  directions  for,  249; 
first  application  of  method  of,  249 ;  so- 
lutions for,  250. 

Water-plants,  size  of,  188;  structure  of 
land-plants  compared  with  that  of, 
257. 

Water-pores,  73. 

Water  tissue,  62,  280. 

Waxv  coatings  upon  the  epidermis,  66. 

White  chlorophyll,  322. 

White  lead  as  a  varnish,  24. 

Wiesner's  tests  for  lignin,  10,  14,  37. 

Wild  plants,  supply  of  nitrogen  to,  334 

Wilting  of  leaves,  471. 

Winterkilling,  472. 

Withering  of  stems,  how  prevented,  263. 

Wood,  autumn,  138,  395;  color  of,  141; 
density  of,  144:  identification  of,  by 
histological  features,  145,  n.;  odor  of, 
142;  preservation  of,  142;  spring,  138, 
396;  structural  characters  of ,  146,  n. 

Wood-cells,  57,  78.  82;  size  of,  86,  n., 
143.  See  also  Trachelds. 

Wood  elements,  inclination  of,  to  the 
axes  of  trees,  14-3. 

Wood-fibre  used  for  paper-pulp,  145. 

Wood-parenchyma,  77. 

Woodward's  carmin,  17. 

Woody  fibres,  57,  W.  See  also  Wood- 
cells. 

Woody  rings,  114,  137;  demarcation 
between,  139  ;  size  of,  140 ;  two, 
formed  in  a  single  year,  139. 

Work  of  the  plant,  185. 


GLOSSARIAL   INDEX. 


Works  of  reference  relating  to  insectiv- 
orous plants,  351;  relating  to  micro- 
scope manipulation  and  micro-chem- 
istry, 24;  relating  to  the  cell  and  its 
modifications,  55;  relating  to  the  his- 
tology of  the  organs  of  vegetation,  165. 

Wounds  of  plants,  healing  of,  150. 


XANTHIC  FLOWER  COLORS  (fa?e6«,  yel- 
low), 454. 


499 

yellow;    4>vMov, 
pds,  dry; 


Xanthophyll    (favflds, 
leaf),  290,  291,  297. 

Xerophilous  plants  (f«pd 
I  love),  280,  n. 

Xylem  (f^,  wood),  104 


ZINC,  occurrence  of,  in  plants,  255;  re- 
lated to  changes  of  form  in  the  plant, 
256. 

Zygophytes,  reproduction  in,  439,  n. 


PRACTICAL   EXERCISES. 


SUGGESTIONS   FOR  STUDIES    IN   HISTOLOGY 
AND   PHYSIOLOGY   OF  PH^ENOGAMS. 


THE  following  hints  are  designed  chiefly  to  aid  students  who 
have  at  their  command  the  simpler  appliances  described  in  the 
foregoing  pages.  In  addition  to  the  simpler  exercises  there  are 
also  suggested  a  few  which  are  quite  within  the  power  of  students 
having  access  to  a  small  chemical  laboratory  and  a  small  cabinet 
of  physical  apparatus.  The  chemical  and  physical  outfits  now 
found  in  many  of  our  high  schools  will  prove  ample  for  the 
successful  prosecution  of  these  experiments. 

HISTOLOGICAL   PRACTICE. 

Material  for  study.  The  supply  of  material  for  histology 
should  be  abundant  and  of  the  best  quality,  all  inferior  or  imper- 
fect specimens  being  carefulty  excluded.  It  (except  that  dis- 
tincth*  referred  to  as  fresh}  should  be  collected  at  proper  seasons 
and  preserved  at  once  in  strong  alcohol,  great  care  being  exer- 
cised to  have  every  specimen  accurately  labelled  ;  name,  locality, 
time  of  gathering,  etc.,  being  noted.  When  alcoholic  material 
is  required  for  immediate  use  in  the  preparation  of  sections,  it 
can  be  softened,  if  necessary,  by  soaking  in  pure  water,  as 
directed  in  37. 

Delineation.  When  a  satisfactory  section  or  preparation  has 
been  secured,  the  student  should  make  an  accurate  drawing  of 
its  essential  features.  The  employment  of  a  camera  lucida  (12) 
insures  correct  proportions  in  all  parts  of  the  sketch,  and  is 
always  to  be  recommended.  Drawings  made  by  its  aid  are  con- 
veniently designated  by  the  following  abbreviated  term,  «d  not. 
del.  It  may  seem  scarcely  necessary  to  caution  students  against 
obscuring  any  part  of  their  histological  sketches  by  meaningless 
shading  ;  a  few  clean  and  clear  outlines  suffice  to  express  the 
character  of  the  preparation  better  than  any  attempt  to  give  the 
effects  of  light  and  shade.  There  are  some  exceptions  to  this 


2  STUDIES   IN   HISTOLOGY. 

broad  statement ;  for  instance,  preparations  of  nascent  flowers 
are  shown  equall}-  well  by  shaded  figures,  and  the  same  is  true 
of  many  pollen-grains,  etc.  The  use  of  slips  of  drawing-paper 
of  uniform  size  and  the  arrangement  of  these  under  appropriate 
heads  will  render  the  keeping  of  a  systematic  record  of  work 
much  easier. 

Permanent  preparations.  In  most  cases  the  sections  or  other 
preparations  should  be  permanently  mounted  in  some  suitable 
preservative  medium,  and  properly  labelled  with  the  name  of  the 
plant  and  of  the  special  part  exhibited,  date  of  preparation, 
medium  in  which  it  is  mounted,  etc.  The  drawings  should  be 
numbered  or  labelled  to  correspond  with  the  permanent  prepa- 
rations. 

Historical  elements,  their  modifications  and  combinations. 
In  the  following  enumeration  of  the  more  important  elements 
the  sequence  is  (1)  form,  (2)  contents,  (3)  distribution,  (4) 
development. 

FORMS  OF  THE   STRUCTURAL   ELEMENTS  AND   SIMPLE 

TISSUES. 
I.    PARENCHYMA  PROPER  AND  ITS  CHIEF  MODIFICATIONS. 

(a)  Soak  a  few  peas  or  beans  in  water  until  they  become  soft 
enough  to  be  cut  without  difficulty,  remove  the  seed-coats,  and 
make  with  a  wet  razor  (see  8)  three  very  thin  sections  through 
the  cotyledons.    These  sections  for  comparison  should  be  at  right 
angles  to  one  another,  in  order  to  exhibit  the  length,  breadth, 
and  thickness  of  the  cells.     On  removing  them  from  the  knife 
or  razor  (by  means  of  a  camel's-hair  brush),  float  them  in  water 
and  move  them  gently  about,  in  order  to  detach  the  cell-contents 
which  have  partly  escaped  from  the  cut  cells.    When  the  sections 
appear  clear,  transfer  them  to  the  middle  of  a  glass  slide,  add 
a  little  pure  water  and  cover  with  thin  glass,  being  very  careful 
to  exclude  all  air-bubbles.     If  the  sections  are  thin  and  wholly 
free  from  bubbles  of  air,  compare  the  outlines  of  the  cells  with 
one  another,  making  drawings  of  the  specimens. 

(b)  Make  similar  sections  (1)  through  the  pulp  of  any  unripe 
fruit  —  apple,  pear,  snow-berry,  etc. ;   (2)  through   the  pith  of 
Elder,  Lilac,  or  any  soft  shoots ;  (3)  through  the  pulp  of  any 
succulent  leaves,   for  instance  those  of  Sedum,  Purslane,  or 
Begonia. 


PARENCHYMA   AND   ITS  MODIFICATIONS.  3 

(c)  Make  a  transverse  and  a  vertical  section  through  the 
petiole  of  any  water-lily,  or  through  the  soft  interior  of  any  rush 
(Juncus). 

(d}  When,  after  considerable  practice,  the  student  succeeds 
in  making  very  thin  sections  of  the  foregoing  plants,  let  the 
reagents  for  the  demonstration  of  cellulose  be  applied  to  them, 
as  directed  in  143. 

It  is  not  superfluous  to  state  (1)  that  success  in  the  application 
of  these  and  most  of  the  other  reagents  employed  under  the 
microscope  is  generally  preceded  by  many  failures,  and  (2)  that 
carelessness  in  the  use  of  some  of  the  reagents  may  irreparably 
ruin  the  microscope  lenses. 

Sclerotic  Parenchyma.  Excellent  material  can  be  obtained 
from  the  flesh  of  pears  and  quinces  (see  211  and  Fig.  40). 

From  the  tough  shells  of  many  sorts  of  nuts  and  seeds  (see 
Fig.  41)  good  preparations  can  be  made  by  the  method  described 
in  495.  For  the  Canada  balsam  there  recommended  good 
shellac  can  be  advantageously  substituted. 

Collenchyma  cells  are  well  exhibited  by  cross-sections  of  the 
stem  of  any  common  Labiate,  for  instance  Spearmint,  or  of  the 
stem  of  almost  any  of  the  Umbelliferae  (see  216).  Apply  dilute 
hydrochloric  acid  to  the  sections. 

Wood  parenchyma  cells  are  easily  obtained  by  careful  macer- 
ation (70).  Dilute  solutions  of  Schulze's  liquid  are  preferable 
to  strong,  although  much  slower  in  action.  Excellent  material 
is  afforded  by  most  of  the  oaks  and  other  hard  woods  (see  254, 
255).  Nearly  all  possible  intermediate  forms  can  be  found  by 
careful  search.  Apply  the  tests  for  "lignin"  (154).  Use  also 
upon  different  specimens  red  and  blue  coal-tar  colors. 

II.    EPIDERMAL  CELLS. 

(a)  Examine  a  film  removed  from  the  upper  surface  of  some 
fleshy  leaf;  for  instance,  Sedum,  the  cultivated  Cotyledon  or 
Eccheveria,  Purslane,  or  Begonia,  etc. 

(ft)  Compare  the  cells  of  this  film  with  those  found  on  the 
upper  surface  of  a  shining  petal;  e.  g.,  that  of  Buttercup  or 
Poppy. 


4  STUDIES    IN    HISTOLOGY. 

(c)  Remove  a  moderately  thin  film  from  the  young  stem  or 
branch  of  some  Cactus,  and  examine  the  exposed  surface  of  the 
epidermal  cells  for  cutinization  (156  and  224).  Apply  any  of 
the  coal-tar  colors  to  similar  fragments,  and  note  differences 
of  tint. 

(d}  Examine  the  "  bloom"  (226)  on  the  following:  (1)  stem 
of  Indian  corn,  (2)  stem  of  castor-oil  plant,  (3)  leaf  of  cabbage, 
(4)  fruit  of  plum,  juniper,  or  Myrica  cerifera  (Baybeny). 

(e)  Make  a  thin  vertical  section  through  the  leaf  of  Ficus 
elastica  (India-rubber  plant),  noting  the  epidermis  and  cystoliths 
(see  164  and  Fig.  6). 

(/)  Examine  the  examples  of  multiple  epidermis  afforded  by 
many  of  the  cultivated  species  of  Begonia. 

Trie-homes,  (a)  Examine  the  velvety  petals  of  any  flower, 
and  compare  their  ver}"  short  trie-homes,  or  hairs,  with  those  on 
downy,  rough,  and  bristly  stems  and  leaves. 

(b)  Examine  also  a  vertical  section  of  a  young  rose-prickle. 
The  variety  of  glandular  trichomes  at  hand   in   any  locality 

is  so  great  that  no  special  directions  need  be  given  for  their 
selection. 

(c)  Root-hairs  are  easily  obtained  by  allowing  the  seeds  of 
flax,  or  the  grains  of  corn,  wheat,  etc.,  to  germinate  on  wet 
filtering-paper,  or  even  on  moist  glass. 

Stomata  (pp.  70-73).  For  the  proper  study  of  these  a  mi- 
crometer eye-piece  (11)  is  very  necessary.  By  its  employment 
the  dimensions  of  individual  stomata  and  the  number  of  stomata 
on  a  given  space  can  be  easily  determined. 

Sections  of  stomata  are  made  best  by  aid  of  the  processes  of 
imbedding  (8).  Examination  of  the  table  by  Weiss  (page  71) 
will  afford  hints  as  to  the  selection  of  large  stomata  for  examina- 
tion in  section. 

Water-pores  and  rifts  (242).  (a)  Water-pores  are  furnished 
by  the  tips  of  the  teeth  of  the  leaves  from  some  species  of  Fuchsia. 
Sections  showing  their  constituent  cells  are  best  made  vertically 
and  lengthwise  through  the  leaf.  Tropaeolum,  or  the  so-called 
Garden  Nasturtium,  also  gives  good  examples. 

(b)  Compare  with  these  water-pores  the  irregular  rifts  in  the 
leaves  of  some  grasses  ;  for  instance.  Indian  corn. 


PROSENCHYMATIC   WOOD-ELEMENTS.  5 

III.   CORK-CELLS. 

For  the  examination  of  these  cells,  the  student  should  begin 
with  the  soft  and  close-textured  "velvet"  cork  procurable  at 
any  apothecary  shop.  Let  the  sections  be  made  in  at  least  two 
directions  at  right  angles  to  each  other,  and  if  possible  let  them 
pass  through  one  of  the  lines  of  demarcation  of  the  cork :  note 
any  differences  of  shape  and  size  presented  by  the  cells  at  that 
place. 

The  young  stems  of  any  of  our  common  currants  give  in  cross- 
section  excellent  illustrations  of  cork-cells  (see  pages  74-76) 
and  of  their  development.  Test  these  and  similar  specimens  of 
cork-cells  for  the  presence  of  cutin  or  suberin  (see  26,  54, 161). 

IV.  PROSENCHYMATIC  WOOD-ELEMENTS. 

These  elements  (see  pages  78-87)  can  be  studied  to  best  ad- 
vantage after  very  careful  maceration,  as  directed  in  70.  Long 
wood-cells,  woody  fibres,  and  tracheae  (or  ducts),  are  easily 
separable  from  each  other  by  such  chemical  means,  and  are 
general!}'  identified  with  facility.  Abundant  material  for  the 
demonstration  of  tracheae  is  afforded  by  the  fibro- vascular  bundles 
(198)  of  herbs  and  by  the  ligneous  parts  of  our  common  trees 
other  than  the  Coniferce.  There  appears  to  be  no  special  need 
of  specifying  the  ligneous  plants  which  can  be  most  successfully 
emploved  for  demonstrations  of  the  woody  elements.  Magnolias, 
Tulip-tree,  woody  Leguminosae  and  Rosaceae,  Urticaceae,  and 
Cupuliferae  are  all  satisfactory  as  sources  of  material. 

Good  examples  of  tracheids  are  procurable  from  species  of 
Coniferae,  such  as  Pines,  Firs,  Spruces,  etc.  These  should  be 
examined  in  all  stages  of  development  and  from  all  points  of 
view,  particular  attention  being  directed  to  the  marked  difference 
between  the  radial  and  tangential  aspects  of  the  cells. 

Cells  which  have  been  separated  from  each  other  mechanically 
and  have  not  been  previously  acted  on  by  chemicals  should  be 
studied  with  reference  to  their  behavior  under  the  action  of 
iodine  and  other  reagents,  it  being  possible  to  demonstrate  the 
existence  of  thin  layers  or  "plates"  which  compose  the  wall. 
Iodine  colors  the  fresh  cells  yellow ;  investigation  shows,  how- 
ever, that  the  inner  wall  or  plate  of  the  cell  is  not  much,  if  at 
all,  colored  by  the  reagent,  the  color  being  confined  to  an  outer 
and  a  middle  wall  or  plate.  When  the  cells  thus  treated  with 
iodine  are  touched  with  concentrated  sulphuric  acid,  the  outer 
and  middle  plates  remain  yellow,  while  the  inner  plate  turns 


6  STUDIES   IN   HISTOLOGY. 

blue.  Soon  the  inner  and  middle  plates  dissolve,  the  outer  not 
being  attacked  until  somewhat  later.  If  Schulze's  macerating 
solution  (full  strength)  is  employed,  the  outer  plate  dissolves 
quickly,  but  the  others  are  not  much  affected  for  some  time. 
Careful  management  of  these  powerful  solvents  is  demanded  to 
insure  even  a  moderate  degree  of  success  in  this  demonstration. 

V.  BAST-FIBRES. 

Isolation  of  these  cells  is  easily  effected  by  teasing  with  needles 
under  the  dissecting  microscope.  The  use  of  macerating  solu- 
tions for  this  purpose  is  also  admissible,  but  the  results  are  not 
quite  so  satisfactory  as  with  the  wood-elements.  Examination 
of  the  table  on  page  90  shows  the  wide  difference  which  exists 
between  the  dimensions  of  the  raw  fibres  and  their  structural 
elements,  into  which  they  can  be  separated  mechanically. 

Most  bast-fibres  take  the  coal-tar  colors  very  well,  and  it  would 
be  best  for  the  student  (without  giving  too  much  time  to  it)  to 
note  the  different  effects  which  are  produced  on  various  fibres  by 
the  colors  described  on  page  19.  The  changes  produced  in  the 
dimensions  of  the  fibres  b}T  dilute  acids  should  also  be  observed. 
After  this  preliminary  practice  the  reactions  given  on  page  90 
should  be  carefully  repeated  with  such  material  as  is  at  hand. 
Full  directions  for  the  preparation  and  use  of  the  prescribed 
reagents  will  be  found  in  the  introductory  chapter.  Lastly,  de- 
terminations of  the  average  dimensions  of  the  commercial  fibres, 
flax,  hemp,  jute,  etc.,  should  be  carefully  made. 

VI.   CRIBROSE-CELLS  OR  SIEVE-CELLS. 

These  can  be  very  easily  demonstrated  in  thin  vertical  sec- 
tions of  the  stems  of  an}*  large  Cucurbitaceous  plants ;  for  in- 
stance, squashes,  melons,  etc.  If  the  student  fails  to  detect  in 
fresh  material  forms  similar  to  those  shown  in  Fig.  73,  a  little 
tincture  of  iodine  should  be  added  to  the  specimen,  in  order  to 
contract  the  lining  and  other  contents  of  the  cells.  By  this 
reagent  the  contents  become  more  or  less  distinctly  colored,  and 
the  discrimination  between  the  cells  and  the  surrounding  tissues 
is  generally  very  plain.  In  other  common  plants,  grape-vines, 
etc.,  the  detection  of  cribrose-cells  is  not  always  easy,  but  a 
diligent  search  will  bring  out  these  characteristic  constituents  of 
soft  bast. 

The  study  of  the  structure  of  the  sieve-plates  requires  the  use 
of  much  higher  powers  of  the  microscope  than  most  beginners 


LATEX-CELLS.  7 

are  likely  to  possess.  Much  can,  however,  be  done  in  the  ex- 
amination of  the  callus  by  the  employment  of  the  reagents 
mentioned  in  282  and  283.  The  student  should  not  fail  to  sub- 
mit a  thin  section  showing  the  larger  cribrose-cells  to  the  action 
of  concentrated  sulphuric  acid,  and  remove  in  this  way  the  whole 
of  the  cell-wall,  leaving  (if  the  manipulation  has  been  careful) 
the  contents  slightly  connected  together  and  showing  the  inter- 
communication between  the  cells. 

VII.  LATEX-CELLS. 

Latex-cells  are  abundant  for  demonstration  in  many  wild  and 
cultivated  plants  ;  but  few  afford  material  better  adapted  to  the 
use  of  beginners  than  the  greenhouse  plant,  Euphorbia  splen- 
dens.  Other  cultivated  species  of  the  same  genus  are  about  as 
good.  With  the  younger  and  softer  steins  of  this  plant  one  has 
merely  to  secure  thin  sections  through  their  outer  or  cortical 
portion,  when,  in  a  good  section,  the  latex-tubes  can  be  found 
ramifying  irregularl}'.  The  peculiar  dumb-bell  shaped  grains  in 
the  tubes  form  a  characteristic  feature. 

When  a  thin  section  of  any  tissue  containing  latex-tubes  is 
gently  heated  in  a  dilute  solution  of  potassic  hydrate,  or  for  a 
shorter  time  in  a  stronger  solution,  the  parts  become  so  much 
softened  that  the  tubes  can  be  easily  separated  from  the  sur- 
rounding tissue,  after  which  they  can  be  floated  on  to  a  fresh 
slide  and  examined  by  themselves. 

Abundant  material  for  the  study  of  latex-cells  is  furnished 
by  plants  of  the  following  groups :  Lobeliaceae,  Campanulaceae, 
Liguliflorse,  and  many  Papaveracese. 

VIII.   SPECIAL  RECEPTACLES  FOR  SECRETIONS. 

These  are  constantly  met  with  in  sections  of  many  stems, 
leaves,  and  fruits.  A  few  examples  for  study  are  here  given. 

(a)  Crystal-cells.    Look  for  these  in  the  leaves  of  the  Aracese, 
Onagraceae,  and  Chenopodiaceae,  and  in  the  bark  of  almost  any 
of  the  ligneous  Rosaceae  (Pomes),  where  they  are  especially 
associated  with  the  bast-fibres. 

(b)  Resin-cells  and  resin-reservoirs  are  found  in  the  bark  of 
many  Conifers-  and  Umbelliferse,  etc.,  in  the  leaves  of  Rutaceae, 
Hypericaceae,  and  Myrtaceae. 

(c)  Tannin  receptacles  are  found  in  very  many  kinds  of  bark. 
For  the  detection  of  tannin,  solutions  of  potassic  chromate  or 
ammonic   chromate   may   be   employed,    a  brown  color  being 


8  STUDIES  IN  HISTOLOGY. 

promptly  produced.     This  test  is  preferable  in  some  respects  to 
the  solutions  of  iron  alluded  to  in  59. 

Intercellular  spaces  of  various  shapes  and  sizes  containing 
air,  or  air  and  water,  are  met  with  in  many  of  the  plants  already 
enumerated.  The  most  interesting  are  found  in  monocotyledo- 
nous  plants,  notably  Aracese  and  Juncacese. 


CELL-CONTENTS. 
I.   PROTOPLASM. 

No  better  material  for  the  demonstration  of  the  physical  and 
chemical  properties  of  protoplasm  in  its  active  state  can  be  em- 
ployed by  a  beginner  than  the  young  stamen-hairs  of  Spiderwort. 
Several  garden  species  of  Spiderwort  are  available  for  this  pur- 
pose, especially  Tradescantia  Virginica  and  pilosa.  The  green- 
house species  can  also  be  employed.  If  none  of  these  are  at 
hand,  an}-  }*oung  large  plant-hairs  with  thin  transparent  walls 
will  answer  for  the  demonstration.  If  the  hairs  are  sufficiently 
young,  the  protoplasm  appears  as  a  nearly  transparent  mass 
filling  the  cell-cavity ;  but  even  when  they  are  onty  slightly 
advanced  in  development  the  mass  becomes  honey-combed  by 
sap-cavities  or  vacuoles.  With  further  development  these  be- 
come confluent,  and  traversed  here  and  there  by  slender  threads  ; 
the  wall  of  the  cell,  however,  as  long  as  it  is  alive,  being  lined 
by  a  delicate  film  of  protoplasm. 

When  the  protoplasm  exists  in  a  cell  only  in  the  latter  condi- 
tion, it  is  well  to  place  the  cell  in  a  solution  of  sugar  (a  five  per- 
cent one  will  answer)  or  in  dilute  glycerin.  By  this  means  the 
protoplasmic  lining  is  contracted  somewhat  b}-  the  withdrawal 
of  water  from  its  cavity,  and  in  shrinking  from  the  wall  its  shriv- 
elled contour  can  be  easity  distinguished. 

It  is  best  for  a  beginner  to  use  in  his  early  demonstrations 
very  young  plant-hairs  in  which  the  vacuoles  do  not  occupy  much 
space  within  the  cell.  The  cells  composing  the  growing  points 
of  most  roots,  stems,  and  leaves  are  too  small  for  satisfactory 
study  at  the  very  outset ;  it  is  well  to  defer  the  examination  of 
the  protoplasm  in  these  until  its  reactions  have  been  clearly 
demonstrated  in  young  plant-hairs. 

Directions  for  the  demonstration  of  active  protoplasm  can  be 
found  in  section  124.  The  tests  there  given  should  be  repeated 
by  the  student  four  or  five  times  with  different  kinds  of  cells. 


PLASTIDS.  9 

after  which  the  effect  upon  fresh  material  of  potassic  hydrate, 
both  the  concentrated  and  the  dilute  solutions,  should  be  care- 
fully watched.  In  these  examinations  it  will  be  well  to  practise 
with  the  reagents  without  lifting  the  cover-glass  (see  17  and  20). 

II.  CHLOKO  PLASTIDS. 

Examine  the  chlorophyll  granules  (see  page  41)  in  the  fol- 
lowing material :  — 

(a)  The  parenchyma  cells  of  any  thick  leaves,  for  instance 
those  of  Purslane,  Begonia,  etc.,  noting  in  the  drawing  the  rela- 
tive size  and  abundance  of  the  granules  in  different  cells. 

(6)  The  epidermis  of  the  same  leaves,  noting  in  what  cells,  if 
an}',  the  granules  are  found. 

Examine  also  the  green  bodies  in  the  leaves  of  any  true  moss, 
and  in  an}-  filamentous  alga,  e.  g.,  Spirogyra,  and  the  cotyledons 
of  the  following  seeds  for  any  green  granules  :  sunflower,  maple, 
and  pine. 

Raise  three  seedlings  of  flax  and  pine.  Let  one  of  the  seed- 
lings of  each  be  kept  in  darkness,  to  the  second  seedling  of  each 
give  only  a  very  little  light,  to  the  third  give  as  much  light  as 
possible  ;  and  when  the  plumules  have  begun  to  develop,  examine 
the  cotyledons  and  young  stems  for  any  color-granules. 

Do  well-blanched  celery  petioles  contain  chlorophyll?  To 
answer  this,  examine  the  base,  middle,  and  summit  of  the  leaf- 
stalk. 

The  next  three  studies  can  be  advantageously  deferred  until 
after  that  of  starch. 

III.  LEUCOPLASTIDS. 

These  bodies  (see  174)  require  for  their  detection  very  careful 
manipulation,  but  by  following  the  directions  given  on  page  44 
they  can  usually  be  made  out  without  much  difficulty.  For  the 
pseudo-bulb  of  Phajus,  which  is  there  recommended,  the  same 
organ  in  almost  any  of  the  cultivated  exotic  orchids  may  be 
substituted. 

IV.  CHROMOPLASTIDS. 

These  can  be  examined  in  any  of  the  colored  fruits;  for 
instance,  in  winter,  the  berries  of  Solanum  Pseudocapsicum 
(Jerusalem  Cherry)  may  be  used  (as  directed  in  498).  The 
granules  there  found  should  be  compared  with  colored  granules 
in  the  petals  of  almost  any  flower.  For  examination  of  the  color- 
granules  in  flowers,  common  pansies  answer  very  well  (see  477.) 


10  STUDIES   IN   HISTOLOGY. 

V.   PROTEIN  GRANULES  (pages  44-47  and  182). 

Examine  thin  sections  of  the  endosperm  of  the  seed  of  Ricinus 
after  the  specimen  has  been  treated  as  directed  in  176,  and  also 
of  the  seed  of  Bertholletia  (Brazil-nut) .  Permanent  preparations 
from  the  latter  should  be  made  as  directed  on  page  47. 

Search  also  for  cubical  crystalloids  in  the  cells  just  under  the 
skin  of  a  potato-tuber. 

VI.    STARCH. 

In  the  examination  of  starch  (pages  47  and  181)  make  thin 
sections  of  (a)  a  potato-tuber,  (b)  the  cereal  grains  figured  in  the 
pages  cited,  (c)  seeds  of  the  pea  and  bean. 

Detach  some  medium-sized  starch-granules  and  measure  them 
with  the  micrometer ;  after  this  apply  a  solution  of  iodine,  em- 
ploying the  most  dilute  one  which  will  impart  a  decided  color  to 
the  granules.  Is  the  color  given  by  iodine  permanent?  Does 
exposure  of  the  colored  specimen  to  light  make  any  difference  in 
permanence  of  color? 

In  all  cases  note  very  carefully  an}-  appearance  of  stratifica- 
tion which  the  different  granules  present,  and  determine  the 
distinctive  characters  b}-  which  each  of  the  common  commercial 
starches  can  be  recognized,  such  as  rice-starch  (toilet-powder), 
laundry  starch  (either  wheat  or  potato),  etc.  After  sufficient 
familiarity  has  been  acquired  by  an  examination  of  all  the 
kinds  of  starch  figured  in  Part  I.,  try  to  identif}1  under  the 
microscope  specimens  of  laundry  starch  and  of  various  kinds 
of  flour. 

Can  starch  be  detected  in  the  following :  — 

Seeds  of  flax  and  mustard  ? 

Roots  of  beets  and  turnips  ? 

Pulp  of  the  ripe  and  the  unripe  apple  ? 

Bark  of  willow  and  maple  ? 

Young  shoots  of  pine  ? 

For  the  detection  of  starch  in  minute  amount  in  chlorophyll 
granules  the  directions  given  on  page  42  must  be  carefully 
followed. 

From  this  time  on,  the  character  of  the  granules  seen  in  any 
specimen  should  be  determined  by  iodine  and  the  result  noted 
in  the  drawing. 


CRYSTALS,   CARBOHYDRATES,   AND  OIL-GLOBULES.     11 

VII.   CRYSTALS. 

In  many  of  the  sections  already  spoken  of,  for  instance  those 
of  Begonia,  single  crystals  and  clusters  of  crystals  have  at- 
tracted attention.  For  a  brief  study  of  different  forms  of 
crystals  (see  pages  52-55)  the  following  are  very  serviceable : 
petioles  of  Begonia,  scales  of  onion,  leaves  of  Tradescantia, 
Fuchsia,  and  the  common  "Calla"  (Richardia),  bark  of  many 
wood}'  plants. 

If  a  thin  section  of  the  leaf  of  almost  any  Araceous  plant,  for 
instance  "  Calla,"  is  placed  in  a  little  water  under  the  micro- 
scope, it  frequently  happens  that  the  discharge  of  acicular 
crystals  (raphides),  described  on  page  52,  can  be  seen  without 
difficulty. 

Apply  to  the  specimens  containing  crystals  the  two  reagents 
spoken  of  in  the  table  on  page  54,  and  carefully  note  results. 

Repeat  Vesque's  experiment  (188). 

VIII.    CARBOHYDRATES  DISSOLVED  IN  THE  CELL-SAP. 

(a)  Inulin  (183)  is  deposited  from  its  solution  in  cell-sap 
whenever  the  cells  are  placed  for  a  time  in  alcohol  or  even  in 
glycerin.  Its  characteristic  forms  are  not  likely  to  be  mistaken 
for  anything  else  met  with  in  the  tissues.  Excellent  material  is 
afforded  not  only  by  the  common  Dahlia,  but  by  Cichory  and 
Dandelion  (see  Fig.  35). 

(V)  The  sugars.  Examine  a  thin  section  of  beet-root  by  the 
method  described  in  184.  Compare  with  it  a  thin  section  of  any 
ripe  fruit. 

IX.    OTHER  CELL-CONTENTS. 

Oil  Globules,  sometimes  of  large  size,  but  generally  minute, 
are  to  be  looked  for  in  those  seeds  which  do  not  contain  starch 
(compare  511).  Examine  in  these  the  effect  of  ether  on  the  par- 
ticles of  oil,  and  also  make  sections  through  the  leaves  of  St. 
John's-wort,  Rue,  and  Dictamnus,  and  through  the  rind  of  an 
orange  or  lemon  to  determine  the  shape  of  the  receptacles  con- 
taining oily  matters. 

Resins,  etc.  For  a  study  of  these,  proceed  as  directed  in  56, 
employing  .young  shoots  of  Pine. 

Tannin,  etc.  For  the  detection  of  tannin,  solutions  of  iron  (see 
59)  may  be  used  ;  but  the  results  are  generally  more  satisfactory 
when  a  solution  of  potassic  or  ammonic  dichromate  is  employed. 
The  color  imparted  to  the  cells  containing  much  tannin  is  brownish 


12  STUDIES   IN   HISTOLOGY. 

or  even  almost  black.  The  student  should  examine  the  very 
peculiar  globules  of  tannin-solution  found  in  the  sensitive  pulvi- 
nus,  or  cushion,  at  the  base  of  the  petiole  of  Mimosa  (Sensitive 
plant).  Similar  globules  have  been  detected  in  different  barks. 

DISTRIBUTION  OF  THE  HISTOLOGICAL  ELEMENTS. 

The  various  histological  elements  after  being  examined  as 
directed  in  Chapter  II.  should  be  investigated  with  regard  to 
their  mutual  relations.  It  is  advisable  to  begin  with  the  skele- 
ton or  framework  of  the  plant,  afterwards  taking  up  the  latex- 
cells,  etc. 

As  shown  in  Chapter  III.,  the  framework  of  the  higher  plants, 
which  we  are  now  to  consider,  consists  of  fibro- vascular  bundles 
variously  arranged  and  conjoined.  The  bundles,  which  in  some 
cases  may  run  for  some  distance  as  isolated  threads,  and  in 
others  exist  as  compact  masses,  are  surrounded  with  larger  or 
smaller  amounts  of  cellular  tissue,  the  exterior  portions  of  which 
are  specially  adapted  to  come  into  contact  with  the  surroundings 
of  the  plant. 

I.    STRUCTURE  OF  FIBRO-VASCULAR  BUNDLES. 

For  the  demonstration  of  the  structure  of  fibro-vascular 
bundles,  seedlings  of  the  following  plants  will  afford  good 
material :  Bean,  Indian  corn,  Castor-oil  plant,  and  Squash.  The 
roots  of  these  plants  give  examples  of  radial  bundles  (313),  in 
which  the  strands  of  liber  and  of  wood  are  in  different  radii, 
while  from  their  stems  (including  the  hypocotyledonary  stem  of 
the  bean,  castor-oil,  and  squash)  may  be  obtained  excellent 
illustrations  of  collateral  bundles. 

The  sections  for  displa3ing  the  structure  of  the  bundles  are 
best  made  in  the  three  directions,  transverse,  vertical-tangential, 
and  vertical-radial.  In  a  few  cases  sections  made  obliquel}-  to 
the  axis  of  the  organ  are  instructive ;  but  unless  great  care  is 
exercised  in  observing  all  their  relations,  the}'  may  be  rather 
misleading. 

In  all  cases  examine  fully  the  character  of  the  bundle-sheath 
(see  212).  The  student  should  not  be  satisfied  with  anything 
less  than  a  clear  interpretation  of  all  the  structural  elements 
which  he  meets  in  a  given  bundle.  If  the  structure  of  a  bundle 
is  not  revealed  by  the  sections  already  prepared,  fresh  ones 
should  be  made  and  carefully  compared  with  the  others,  and 


FIBRO-VASCULAR   BUNDLES.  13 

with  the  figures  in  Part  I.  In  order  to  identify  some  of  the 
structural  elements  composing  a  bundle,  it  is  sometimes  advis- 
able to  resort  to  cautious  maceration  (see  70),  so  that  the  parts 
may  be  isolated.  It  has  been  found  advantageous,  in  a  few  in- 
stances, to  very  securely  fasten  the  section  under  examination  to 
thin  rubber  membrane  by  means  of  the  best  "  rubber"  cement 
or  marine  glue,  and  then  subject  the  membrane  and  section  to- 
gether to  the  action  of  the  macerating  liquid,  great  care  being 
exercised  to  have  the  process  gradual.  After  the  maceration  is 
complete,  the  membrane  is  removed  from  the  liquid,  washed, 
and  then  slowly  stretched  until  the  adherent  wood-elements  are 
somewhat  torn  apart.  It  will  be  observed  that  by  this  method 
their  former  relations  need  not  be  greatly  disturbed. 

After  examining  the  fibro-vascular  bundles  in  the  seedlings 
above  named,  proceed  to  the  study  of  the  bundles  in  the  roots, 
stems,  and  leaves  of  two  adult  herbaceous  plants,  for  instance 
Indian  corn  and  Bean,  in  order  to  ascertain  what  differences,  if 
any,  exist  in  the  composition  of  the  bundles  in  a  given  organ  at 
different  periods  of  growth. 

It  was  stated  in  309  that  the  simplest  form  of  a  fibro-vascular 
bundle  consists  of  merely  a  few  tracheal  cells  (or  sometimes  tra- 
cheae) together  with  some  cribrose  or  sieve  cells.  The  student 
should  search  for  tracheids,  which  may  occur  disconnected  from 
any  bundle  ;  as  for  example  in  the  stems  of  species  of  Salicornia 
(a  seaside  plant  of  succulent  texture),  and  in  the  petiole  and 
pitchers  of  Nepenthes.  Tracheids  occur  also,  often  in  a  con- 
tinuous layer,  as  a  sheath  of  the  aerial  roots  of  orchids.  Sieve- 
tubes  may  be  looked  for  at  a  little  distance  from  the  bundles  in 
the  stems  of  potato  and  tobacco,  where  they  occur  in  the  periphery 
of  the  pith. 

Two  supplementary  studies  are  strongly  advised :  (1)  of  the 
bundles  in  tVrns,  (2)  of  those  in  aquatic  phaenogams.  In  the 
former,  "  conc-entric  "  bundles  are  met  with  ;  in  the  latter,  rudi- 
mentary bundles. 

II.      COUESE  OF  THE  BUNDLES. 

The  course  of  the  fibro-vascular  bundles  can  be  traced  in  some 
cases,  especially  in  young  and  rather  juicy  stems,  like  those  of 
Impatiens,  with  little  or  no  difficulty ;  but  it  is  generally  neces- 
sary to  treat  somewhat  thick  sections  of  the  stem  under  ex- 
amination by  a  macerating  liquid,  for  instance  potassic  hydrate, 
after  which  the  course  can  be  made  out.  In  most  cases  the 
course  of  the  bundles  can  also  be  made  out  by  series  of  sections 


14  STUDIES   IN   HISTOLOGY. 

made  at  different  points  in  the  organ,  care  being  taken  to  arrange 
the  sections  in  their  proper  sequence. 

The  following  material  will  be  useful  for  practice  in  the  deter- 
mination of  the  course  of  the  bundles  :  young  shoots  of  Clematis, 
Vitis,  and  Phaseolus  (all  dicotyledons)  ;  and,  after  these,  shoots 
of  Spiderwort,  the  rootstock  of  Convallaria  (Lily  of  the  Valley), 
or  of  Smilacina,  and  if  possible  the  bud  of  a  young  palm. 

The  course  of  the  bundles  in  leaves  and*  dry  fruits  can  be 
easily  demonstrated  by  "  skeletonizing  "  them.  This  is  effected 
by  keeping  the  leaves  for  a  long  time  in  a  dilute  solution  of 
calcic  hypochlorite  (see  50). 

DEVELOPMENT  OF  THE  ELEMENTS. 

This  must  be  examined  in  the  youngest  seedlings  of  the  plants 
now  spoken  of.  The  sections  must  be  through  the  growing 
points,  and  should  be  well  cleared  bj-  one  of  the  processes  de- 
scribed in  16  or  24.  For  the  development  of  special  structural 
elements,  for  example  latex-cells,  see  Part  I. 

HISTOLOGY  OF  THE   VARIOUS  ORGANS. 

I.    THE  ROOT. 

The  student  may  use,  for  demonstration  of  the  histology  of 
the  root-tip,  an}'  seedlings  which  have  been  grown  either  in  water 
or  on  a  clean  support,  and  are  therefore  free  from  grains  of 
earth.  Root-hairs  are  best  examined  on  seedlings  sprouted  upon 
moist  sponge  or  bibulous  paper. 

II.    THE  STEM. 

It  is  advised  that  the  student  now  prepare,  in  addition  to  the 
sections  of  stems  previously  examined,  sections  through  two  and 
three  year  old  shoots  of  any  common  dicotyledon,  and  note  all 
differences  which  exist  between  the  different  woody  elements 
forming  the  rings,  and  all  changes  in  the  bast.  The  growth  of 
cambium  should  be  carefully  examined  in  the  young  shoots  of 
Pine  and  of  Oak. 

For  the  study  of  the  secondary  changes  in  the  bark,  the 
twigs  of  black  currant  or  of  white  birch  afford  good  material, 
the  successive  changes  being  easily  followed. 

The  occurrence  of  true  cork  in  out-of-the-way  places  is  illus- 
trated by  Catalpa,  Professor  Barnes  reporting  that  it  sometimes 
occurs  between  the  annual  layers  in  the  stem  of  Catalpa  speciosa. 
Other  cases  should  be  looked  for. 


LEAF   AND  FLOWER.  15 

III.    THE  LEAF. 

The  leaf  presents  few  difficulties  in  histological  manipulation 
For  all  necessary  details  consult  pp.  155-164.  The  following 
plants  atford  excellent  material  for  study : 

Of  the  centric  arrangement  of  parenchyma  in  the  blade,  Trit- 
icum  vulgare,  Acorns,  and  many  of  the  Cactacese. 

Of  the  bifacial  arrangement  of  parenchyma,  many  plants  with 
flat  horizontal  leaves. 

IV.    THE  FLOWEK. 

It  is  assumed  that  the  student  has  thoroughly  familiarized 
himself  with  the  morphology  of  the  simpler  flowers  as  explained 
in  Volume  I.,  and  has  acquired  some  facility  in  examining,  as 
there  directed,  those  of  more  complicated  structure. 

The  study  of  the  microscopic  anatomy  of  all  the  floral  organs 
in  their  adult  state  should  precede  any  attempt  to  examine  their 
development.  Since  the  flower  should  be  examined  in  all  stages 
of  its  development,  it  is  well  to  select  for  study  only  those  flow- 
ers which  can  be  readily  obtained  in  large  numbers,  and  further- 
more, by  preference,  those  which  are  not  thickly  covered  with 
hairs.  The  common  weeds  Lepidium  Virginicum  and  Capsella 
Bursa-pastoris  afford  excellent  material  for  the  study  of  the 
flower  and  its  development,  and  have  the  signal  advantage  of 
being  much  alike  in  the  most  essential  respects,  yet  possessing 
minor  differences  which  are  not  likely  to  be  overlooked. 

An  exhaustive  examination  of  the  histology  of  the  organs  of 
the  flower  should  begin  with  the  study  of  the  sepals,  the  other 
organs  being  taken  up  in  their  turn,  and  the  following  points 
receiving  special  attention :  (1)  the  possible  occurrence  of  stom- 
ata  upon  all  the  parts  of  the  blossom ;  (2)  the  peculiarities  in 
the  proper  epidermal  cells  of  the  petals  ;  (3)  the  character  of  the 
parenchyma  in  all  parts  of  the  flower,  and  all  differences  in  the 
nature  of  the  cell  contents,  notably  the  plastids  ;  (4)  the  charac- 
ter and  the  distribution  of  the  fibro-vascular  bundles  in  their 
course  from  the  pedicel  to  their  ultimate  attenuated  ramifications 
in  the  several  organs. 

Stamens.  The  character  of  the  pollen  demands  special  atten- 
tion, and  its  examination  should  be  followed  by  a  comparison 
between  as  many  kinds  as  possible  taken  from  various  flowers. 
The  character  of  the  integuments  and  the  contents  of  the  grains 
should  also  be  demonstrated. 


16  STUDIES   IN   HISTOLOGY. 

The  pistil  requires  little  special  study,  except  in  regard  to  its 
development.  It  will  be  well  to  examine  the  conductive  tissue 
of  the  style  and  trace  it  down  to  the  ovarian  walls.  (Other 
minute  matters  connected  with  the  stamens  and  pistils  are  con- 
sidered under  "Fertilization.") 

V.  DEVELOPMENT  OF  THE  FLOWER. 

From  the  youngest  flower-cluster  of  any  plant  having  indeter- 
minate inflorescence,  for  instance  that  of  Lepidium  or  Capsella, 
cut  squarely  off  a  short  piece  of  the  tip,  place  it  on  a  glass  slide 
in  a  little  alcohol,  in  order  to  remove  the  air,  and  cover  with 
thin  glass.  (If  the  student  has  an  air-pump,  the  specimen  can 
be  placed  at  once  in  water  on  the  slide,  and  then  subjected  to 
the  action  of  a  partial  vacuum,  which  will  of  course  free  the 
whole  preparation  from  any  air-bubbles.)  After  the  air  has 
been  removed,  add  water,  and  if  the  specimen  requires  clearing, 
as  is  usually  the  case,  some  potassa.  On  gently  warming  the 
slide  the  specimen  will  grow  somewhat  darker,  but  after  a  time 
will  be  made  tolerabty  clear.  If  not,  proceed  as  directed  in  25. 
The  specimen,  if  a  good  one  and  well  prepared,  ought  to  show 
all  the  relations  of  the  several  flowers  of  the  cluster  to  each 
other.  Prepare  a  second  specimen  by  removing  the  flowers  in 
succession  under  the  dissecting  lens,  beginning  with  the  larger, 
and  placing  them  in  a  row  which  will  comprise  all  the  stages  of 
development.  With  the  material  thus  obtained,  which  it  is  well 
to  keep  moist  with  glycerin,  the  examination  of  all  the  different 
parts  can  be  successfully  carried  out.  The  stud}-  will  be  far 
more  instructive  if  the  student  makes  a  parallel  series  with  an 
allied  species.  Comparison  of  the  two  species  above  mentioned 
shows  exactly  when  and  where  some  of  the  parts  are  arrested  in 
development. 

VI.  DEVELOPMENT  OF  THE  POLLEN. 

The  examination  of  the  anther  for  this  study  should  begin  at 
a  very  early  stage  in  the  growth  of  the  flower,  and  particular 
attention  should  be  given  to  the  cells  which  line  the  pollen  cavi- 
ties. Great  advantage  is  gained  from  the  skilful  employment 
of  staining  agents,  by  which  the  parts  are  brought  out  more 
clearly  (see  77  et  seq.\  All  changes  in  the  character  of  the 
nucleus  of  the  grains  during  their  differentiation  demand  for 
their  identification  the  use  of  staining  agents  without  the  pre- 
vious application  of  potassa. 


STBUCTURE   OF   THE   SEED.  17 

VII.    DEVELOPMENT  OF  OVULES. 

In  this  examination  the  wall  of  the  ovary  must  be  removed, 
and  the  minute  eminences  which  are  to  become  the  ovules  ob- 
served in  their  earliest  stage.  The  successive  external  produc- 
tions which  are  to  become  the  integuments  of  the  ovule  should 
be  traced  with  great  care.  It  is  also  well  to  examine  minutely 
the  changes  in  form  of  the  embryonal  sac  in  the  nucleus  (or 
nucellus)  of  the  ovule.  These  will  be  further  adverted  to  under 
"  Fertilization." 


VIII.     MINUTE  STRUCTURE  OF  THE  SEED. 

Since  in  the  previous  exercises  some  parts  of  the  seed  have 
been  already  examined,  it  is  necessary  here  merely  to  call  atten- 
tion to  the  desirability  of  studying  the  character  of  the  integu- 
ments in  at  least  two  common  and  a  few  exceptional  cases. 
For  the  former,  no  seeds  are  better  than  those  of  the  common 
Bean,  Pea,  or  Lupine.  After  a  clear  idea  has  been  obtained  of 
the  nature  of  the  cells  which  compose  the  greater  part  of  the  two 
integuments,  the  student  should  make  careful  sections  through 
the  hilum  in  order  to  display  the  peculiar  sac-like  body  there 
seen.  For  the  exceptional  types  of  integuments,  examine  the 
seeds  of  Flax  (showing  the  gelatinous  modification,  etc.),  or 
better,  if  they  can  be  procured,  the  seeds  of  Collomia  and  Cot- 
ton. It  will  be  well  also  to  examine  the  closely  united  ovarian 
and  ovular  coats  in  the  common  grains,  like  Wheat  or  Indian 
corn. 

The  student  should  examine  as  many  seeds  as  possible,  includ- 
ing those  containing  much,  little,  and  no  starch,  and  observe  also 
whether  or  not  there  is  any  difference  between  ripe  and  unripe 
seeds  in  the  amount  of  starch  which  they  contain.  He  should 
examine  the  contents  of  the  cells  nearest  the  integuments  in  any 
of  the  seeds  above  mentioned,  and  ascertain  the  relative  amount 
of  albuminoid  matters  present  compared  with  those  in  the  cells 
in  the  interior  of  the  seed. 

Further  microscopic  examination  of  the  seed  is  to  be  taken  up 
when  germination  is  studied. 


18  STUDIES   IN   PHYSIOLOGY. 


PRACTICAL    EXERCISES    IN    VEGETABLE 
PHYSIOLOGY. 

This  course  of  experiments  in  Vegetable  Physiology  is  divided 
into  two  parts :  the  first  series  comprises  a  few  exercises  which 
can  be  undertaken  by  any  one  having  only  the  simplest  appli- 
ances; the  second  requires  more  complicated  apparatus.  The 
first  series,  if  faithfully  and  intelligently  followed,  should  place 
the  student  in  possession  of  the  leading  facts  regarding  the  prin- 
cipal activities  of  the  plant ;  while  the  second  series  should  ac- 
quaint him  with  the  chief  methods  employed  for  the  investigation 
of  the  special  offices  of  the  organs  of  the  plant,  and  fix  the 
principal  results  in  his  mind.  It  should,  however,  be  frankly 
stated  that  for  the  proper  and  satisfactory  performance  of  the 
experiments  detailed  in  this  second  or  special  series  the  student 
should  first  become  familiar  with  the  ordinary  methods  of  chemi- 
cal and  ph3'sical  manipulation,  and  have  at  command  the  funda- 
mental principles  of  chemistry  and  of  physics. 

FIRST  SERIES. 

In  this  series  are  discussed  experimentally  the  following  car- 
dinal topics:  (1)  The  behavior  of  protoplasm  in  a  living  cell; 
(2)  The  gain  in  substance  by  assimilation  and  the  loss  of  sub- 
stance by  growth  ;  (3)  The  chief  conditions  under  which  plants 
assimilate  ;  (4)  The  dependence  of  the  principal  activities  of  the 
plant  upon  certain  external  conditions. 

The  experiments  can  be  conducted  with  the  following  ap- 
pliances :  — 

1.  A  small  balance  with  weights  ranging  from  twenty  grams 
to  one  centigram.    If  a  balance  is  not  procurable,  ordinary  hand- 
scales  with  horn  or  brass  pans  will  answer  very  well. 

2.  A  water-bath,  or  in  place  of  it  a  small  porcelain-lined 
kettle  of  one  or  two  pints  capacity,  fitting  into  a  larger  iron 
kettle.     Water  placed  in  the  larger  kettle  prevents  the  inner  one 
from  being  heated  above  the  boiling-point  of  water. 

3.  Half  a  dozen  test-tubes. 

4.  Three  or  four  pieces  of  glass  tubing,  six  inches  long. 

5.  A  small  camel's-hair  pencil,  and  India  ink. 

<>.  Pieces  of  colored  glass  or  colored  gelatin  (red,  yellow, 
green,  blue,  violet),  six  inches  square  or  larger. 


MOVEMENTS   OF  PROTOPLASM.  10 

For  the  first  study,  the  examination  of  protoplasm,  a  micro- 
scope magnifying  from  two  hundred  to  six  hundred  diameters 
will  be  required,  together  with  a  small  outfit  of  slides  and  covers  ; 
and  for  the  examination  of  growth  a  zinc  box  constructed  as 
directed  in  "The  Dependence  of  Growth  upon  Heat." 

I.    THE  BEHAVIOR  OF  PROTOPLASM  IN  A  LIVING  VEGETABLE  CELL. 

For  all  necessary  details  as  to  the  chemical  reactions  of  proto- 
plasm, see  124  and  the  exercise  on  page  8  of  this  "Praxis." 
At  present  it  is  proposed  to  call  attention  to  the  various 

Movements  of  Protoplasm. 

(a)  Material.     The  delicate  hairs  from  the  young  leaves  of 
almost  any  pubescent  plant  will  serve  for  the  demonstration 
of  these    movements,   but  the  following  are  recommended  on 
account  of  their  abundance  and  excellence :    stamen-hairs   of 
Spiderwort   (Tradescantia),   hairs   from   the  young   leaves  of 
squash  and  nettle,  and  from  the  velvety  leaves  of  many  culti- 
vated exotics. 

( b)  Preparation  of  specimens.     Remove  by  needles,  forceps, 
or  scalpel  a  very  little  of  the  epidermis  with  its  attached  hairs, 
and  place  it  at  once  in  a  little  water  on  a  glass  slide.    In  placing 
the  thin  glass  cover  on  the  specimen  be  careful  to  exclude  all  air- 
bubbles  and  not  to  crush  the  cells.    If  necessary,  put  a  fragment 
of  glass  under  one  edge  of  the  cover,  to  lighten  the  pressure  on 
the  object.     If  the  hairs  are  suitable  for  the  examination,  the 
delicate  threads  of  protoplasm  ought  to  be  distinctly  seen  through 
the  cell-walls,  and,  after  a  little  time,  a  movement  of  translucent 
granules  should  be  seen  in  them.     If,  after  a  few  moments,  no 
movement  can  be  detected,  warm  the  slide  a  little  with  the  hand 
and  again  observe.     If  no  movement  should  now  be  seen,  add 
to  the  water  on  the  slide  a  little  dilute  glycerin ;  this  causes 
slight  contraction  of  the  protoplasmic  lining  of  the  cell,  and 
probably  the  movement  can  then  be  observed  in  the  threads.    If 
not,  do  not  waste  time  over  the  specimen,  but  try  a  fresh  one.  A 
power  of  200  diameters  will  answer  for  this  work,  but  one  of  500 
is  better. 

(c)  Questions  to  be  answered  by  the  specimen.    If  the  student 
has  secured  a  good  preparation,  in  which  the  movement  of  gran- 
ules in  the  threads  can  be  seen  distinctly,  he  can  easily  answer 
the  following  queries :  What  is  the  rate  of  motion  of  the  gran- 
ules at  the  temperature  of  the  room?    Do  the  threads  remain 


20  STUDIES   IN   PHYSIOLOGY. 

unchanged  in  shape?  Do  any  granules  pass  from  one  cell  to  the 
next  one?  Where  is  the  motion  fastest? 

While  the  observations  are  in  progress,  be  careful  not  to  allow 
the  preparation  to  become  dry :  add  a  little  water  occasionally, 
and  note  whether  the  rate  of  motion  is  increased  or  diminished 
for  the  next  minute  or  so. 

(d)  Questions  to  be  answered  by  experiment.  (1)  What  effect 
upon  the  rate  of  protoplasmic  movement  does  increase  of  tem- 
perature produce? 

In  order  to  keep  the  slide  with  the  specimen,  prepared  as 
above,  from  touching  the  metallic  stage  of  the  microscope,  place 
under  each  end  of  it  a  piece  of  thick  pasteboard,  and  then  clamp 
it  down  firmly  by  means  of  the  stage-clips,  so  that  it  cannot 
be  easily  displaced.  After  the  slide  has  been  in  position  for  a 
few  minutes,  note  the  rate  of  movement  of  the  granules  at  the 
ordinary  temperature  of  the  room.  When  this  has  been  accu- 
rately determined,  place  near  the  specimen,  on  the  slide,  a  coin 
or  other  small  piece  of  metal  which  has  been  heated  to  40°  C., 
and  note  the  change  of  rate.  Afterwards  apply  more  and  more 
heat  03*  a  second  and  a  third  application  of  the  coin,  heated  each 
time  higher  by  immersion  in  hot  water,  and  note  the  result.  Of 
course  this  very  simple  method  of  experiment  does  not  allow  one 
to  determine  the  exact  temperature  to  which  the  specimen  is 
heated,  but  its  temperature  is  only  a  little  lower  than  that  of  the 
coin. 

For  exact  experiments  employ  the  apparatus  described  in 
557  or  558. 

(2)  What  effect  upon  the  rate  of  movement  does  a  decrease  of 
temperature  cause? 

Prepare  a  fresh  specimen  as  directed  under  (6),  lower  the  tem- 
perature of  the  slide  by  the  application  of  a  coin  which  has  been 
immersed  in  ice-water,  and  note  all  changes  in  the  rate  of  move- 
ment. Still  lower  temperatures  are  easily  secured  by  placing  in 
a  small  copper  cup  on  the  slide  (an  ordinary  copper  cartridge- 
shell  answers  very  well)  a  mixture  of  ice  and  salt. 

If  in  either  of  the  preceding  experiments  the  motion  of  the 
granules  has  been  arrested,  endeavor,  b}-  reversing  the  applica- 
tion, to  re-establish  movement :  thus,  if  the  movement  was  ar- 
rested at  the  higher  temperature,  apply  cold  ;  if  it  was  arrested  by 
cold,  apply  heat. 


ASSIMILATION   AND  GROWTH.  21 

II.    THE  GAIN  IN  SUBSTANCE  BY  ASSIMILATION,  AND  THE  Loss  OF  SUB- 
STANCE DURING  GROWTH. 

Select  a  number  of  beans  (Windsor,  Horticultural,  Lima,  or 
white),  of  nearly  the  same  size,  weigh  ten  of  them,  and  dry  them 
carefully  in  a  water-bath  to  ascertain  the  amount  of  water  which 
they  contain.  Take  two  other  lots  of  ten  each,  weigh  them 
carefully,  plant  them  on  moist  blotting-paper  or  wet  sponge,  and 
keep  them  in  a  warm  place  until  they  have  sprouted.  When 
the  beans  have  fairly  started,  suspend  them  over  the  surface  of 
water,  with  their  roots  in  it,  as  directed  in  669.  From  this  time 
on,  keep  one  set  of  the  seedlings  in  the  light  and  the  other  set 
in  the  dark,  being  careful  in  each  case  that  the  water  is  supplied 
in  sufficient  quantity  to  make  up  for  all  loss  by  evaporation,  and 
that  it  is  changed  every  third  day.  Let  all  the  conditions  under 
which  the  two  sets  are  cultivated  be  as  nearly  alike  as  possil  3, 
with  the  single  exception  that  light  is  present  in  one  case  add 
completely  absent  in  the  other.  In  a  couple  of  weeks  the  two 
sets  of  seedlings  will  have  become  large  enough  for  further 
study  :  the  set  grown  in  the  light  will  be  green  and  thrifty,  the 
others  may  be  as  large,  but  they  will  have  a  yellow,  unhealthy 
appearance.  Remove  the  two  sets  from  the  water  and  carefully 
dry  them  separately  over  the  water-bath  as  directed  in  the  case  of 
the  seeds.  When  they  do  not  further  lose  weight,  weigh  carefully. 
Compare  the  weight  of  the  dried  seedlings  with  the  weight  o 
the  dried  seeds. 

III.     THE  CHIEF  CONDITIONS  OF  ASSIMILATION. 
In  the  examination  of  these,  repeat  with  great  care  the  exper 
ments  detailed  on  page  305. 

IV.  THE  DEPENDENCE  OF  GROWTH  UPON  HEAT. 
This  may  be  shown  in  the  following  manner :  Take  a  sheet  o. 
tin  or  zinc  about  6  to  8  inches  in  width  and  24  inches  in  length. 
Turn  up  its  ends  at  right  angles  6  inches.  Turn  them  once 
more  at  right  angles,  rather  less  than  half  an  inch  at  the  top 
and  two  and  a  half  inches  at  the  bottom.  This  last  turn  will 
hold  a  sheet  of  glass  which  will  form  the  fourth  side  of  a  box: 
narrower  by  two  inches  at  the  bottom  than  at  the  top  ;  that  is, 
the  glass  side  will  not  be  vertical,  but  inclined.  Cut  out  a  piece 
of  wire-gauze  of  the  right  size  for  the  bottom,  and  either  solder 
or  rivet  it  in  place.  Fill  this  box  with  well-moistened  sawdust. 
Plant  a  row  of  six  or  eight  large  Windsor  beans  in  regular  order 


22  STUDIES   IN   PHYSIOLOGY. 

in  the  sawdust,  near  the  glass  side,  so  that  the  tip  of  each  radicle 
will  start  down  about  one  fourth  of  an  inch  from  it.  If  the  glass 
is  properly  inclined,  the  radicle  will  quickly  press  itself  against 
it  and  thus  be  the  more  readily  seen  and  studied  in  its  subse- 
quent growth.  When  the  radicles  are  about  two  inches  in 
length,  withdraw  them,  and  by  the  aid  of  a  fine  camel's-hair 
brush  and  India  ink  mark  them  off  with  precision  at  regular 
intervals  of  one  or  two  millimeters,  then  place  each  in  the  same 
place  and  position  from  which  it  was  taken.  It  will  be  found 
that  only  their  tips  grow ;  the  marks  above  the  tips  remaining 
the  same  distance  apart. 

Put  a  thermometer  in  the  sawdust  in  order  to  observe  the  tem- 
perature, upon  which  it  will  be  found  the  rate  of  growth  depends. 
Place  the  seedlings  near  the  stove  or  over  a  register  where  the 
temperature  of  the  sawdust  can  be  gradually  raised  to  from  28° 
to  30°  C.  Having  previously  measured  and  noted  the  exact 
length  of  the  radicle  of  each  plant,  observe  its  increase,  while 
the  temperature  remains  constant,  for  a  given  period  of  say  from 
five  to  ten  hours.  Next  place  the  case  containing  the  seedlings 
in  an  improvised  ice-chest  (any  box  which  can  be  well  closed  will 
answer),  and  when  the  temperature  has  been  reduced  to  10°  C., 
or  nearly  that,  measure  the  roots  care  full}-  again.  Hold  this 
degree  of  cold  as  nearly  constant  as  possible  for  five  or  ten  hours, 
whichever  may  have  been  the  period  of  time  in  the  first  case. 
Compare  the  growtli  in  the  two  periods  and  note  the  difference. 


SECOND  SERIES. —SPECIAL  EXPERIMENTS. 

I.  DIFFUSION. 

Place  a  tumbler  containing  an  inch  or  two  of  pure  water  upon 
a  firm  shelf  where  it  will  not  be  subject  to  any  jarring,  and  put 
in  it  a  vial  filled  to  the  brim  with  some  colored  liquid,  for  instance 
blue  or  purple  ink.  Then  by  means  of  a  tube  or  "  thistle-funnel " 
resting  on  the  bottom  of  the  tumbler  pour  into  the  tumbler  water 
enough  to  come  up  to  the  mouth  of  the  vial,  and  very  cautiously 
add  more  until  the  mouth  is  covered  to  a  depth  of  about  an  inch. 
If  the  pouring  has  been  skilfully  done,  there  will  be  scarcely  any 
of  the  ink  mixed  with  the  surrounding  water.  Let  the  apparatus 
stand  undisturbed  for  a  week  or  so,  and  note  any  changes  in  the 
color  which  may  be  observed  from  day  to  day. 

Try  the  same  experiment  with  a  saturated  solution  of  common 
salt  in  place  of  the  ink,  and  at  intervals  of  three  days  cautiously 


OSMOSE.  23 

remove  a  little  of  the  water  from  the  bottom  of  the  tumbler  by 
means  of  a  small  tube  or  pipette,  and  test  it  for  chlorides. 

II.    OSMOSE.    DIFFUSION  THROUGH  A  MEMBRANE. 

Scoop  out  a  small  cavity  in  a  fleshy  root,  for  instance  that  of 
a  carrot,  and  carefully  dry  it  with  a  cloth.  Then  fill  it  with  fine 
sugar,  and  let  the  root  stand  in  some  place  where  it  will  not 
be  disturbed.  Note  any  changes  which  take  place  in  the  sugar 
and  in  the  condition  of  the  root.  By  comparative  examinations 
of  the  tissues  removed  and  those  remaining,  ascertain  whether 
any  of  the  sugar  has  entered  the  cells. 

Tie  a  thin,  sound  piece  of  parchment  paper  (or,  better  still, 
parchment)  over  the  mouth  of  a  thistle-funnel,  and  fill  the  bulb 
of  the  funnel  with  a  strong  solution  of  common  salt.  Then  sus- 
pend the  funnel  in  pure  water,  so  that  the  level  of  the  water 
outside  corresponds  to  that  of  the  brine  inside,  and  keep  the  ap- 
paratus in  a  warm  place,  noting  any  change  of  level  of  the  liquid 
in  the  funnel  tube.  Try  other  substances  in  the  tube ;  for  in- 
stance, dilute  potassic  hydrate,  concentrated  potassic  hydrate, 
syrup,  and  dry  powdered  gum-arabic. 

Carefully  examine  the  upper  surface  of  the  leaf  of  Lilac,  Olean- 
der, or  Echeveria  for  the  presence  of  stomata,  and  if  none  are 
found,  make  the  following  trial  with  a  good,  sound,  young  leaf, 
being  careful  to  see  that  the  plant  is  well  watered.  Put  a  drop 
of  water  on  the  upper  surface  of  the  leaf,  and  dust  upon  it 
either  finely  powdered  sugar  or  salt,  until  the  drop  has  taken 
up  all  it  can,  and  the  mass  looks  nearly  dry ;  then  blow  off  the 
residue,  and  cover  the  leaf  or  plant  with  a  bell-jar.  Keep  it  in 
a  warm  place  and  water  well.  Observe  in  the  course  of  a  few 
hours,  and  at  frequent  intervals  during  the  next  four  or  five  days, 
any  changes  which  the  spot  of  sugar  undergoes.  It  is  a  good 
plan  to  prepare  several  such  spots  with  different  substances. 

III.  PELLICLE  PRECIPITATES.  —  TRAUBE'S  ARTIFICIAL  CELL. 
Dissolve  5  grams  of  pure  potassic  ferrocyanide  in  100  cubic 
centimeters  of  pure  water.  Place  some  of  the  solution  in  a  test- 
tube  having  a  foot,  and  drop  into  the  tube  a  small  fragment  of 
moist  chloride  of  copper.  Observe  the  changes  which  take  place 
in  the  shape  of  the  film  which  instantly  forms  around  the  frag- 
ment. Try  the  same  experiment  with  a  saturated  solution  of 
potassic  ferrocyanide,  and  afterwards  with  solutions  containing 
respectively  1  and  10  per  cent  of  the  ferrocyanide. 


24  STUDIES   IN    PHYSIOLOGY. 

What  effects  are  produced  when  a  solution  of  potassic  ferro- 
cyanide  is  shaken  up  with  a  solution  of  copper  chloride? 

The  pellicle  precipitates  can  be  further  examined  as  directed  on 
page  226.  Calcic  chloride  and  sodic  carbonate  can  be  employed 
in  the  examination  instead  of  the  substances  there  mentioned. 

IV.     PFEFFER'S  ARTIFICIAL  CELL. 

Repeat  Pfeffer's  experiments  (page  227),  with  all  the  precau- 
tions there  advised. 

In  every  case  where  a  manometer,  or  pressure-gauge,  is  to  be 
used,  corrections  must  be  made  for  temperature  and  for  baro- 
metric pressure  according  to  the  directions  given  in  such  works 
as  Bunsen's  "  Gasornetr}-." 

V.     ABSORPTION  OF  WATER. 

Moisten  one  side  of  a  perfectly  flat,  thin  piece  of  hard  wood, 
for  instance  the  holly-wood  used  for  scroll-sawing,  and  note 
any  change  of  form  which  occurs.  What  effect  is  produced  by 
moistening,  in  the  same  way,  the  other  side  of  the  wood  ? 

Fill  a  strong  stone  bottle  with  large  dry  seeds  of  known  weight, 
for  instance  beans,  and  put  it  in  a  pail  of  water  so  that  the 
water  can  pass  into  its  mouth.  If  the  bottle  should  break  in  a 
few  hours,  remove  quickly  with  blotting-paper  all  the  outside 
moisture  from  the  seeds,  and  determine  their  increase  in  weight 
due  to  absorption  of  water. 

Place  a  thermometer  bulb  in  a  tumbler  half  full  of  dry  starch  ; 
slowly  add  to  this  water  of  exactly  the  same  temperature,  and 
note  any  change  of  temperature  which  accompanies  the  absorp- 
tion of  the  water  by  the  starch. 

Weigh  a  fleshy  root,  and  carefull}*  dry  it  in  a  water- bath,  to 
determine  the  amount  of  water  which  can  be  expelled  at  100°  C. 
Then  raise  the  temperature  of  the  root  to  somewhat  above 
100°  C.,  by  carefully  heating  it  in  a  sand-bath,  and  observe  any 
loss  of  weight.  Determine  also  the  amount  of  water  contained 
in  a  fibrous  root  of  Indian  corn,  a  small  woody  stem,  "  dry  " 
wood,  leaves  of  Indian  corn,  Begonia,  and  Sedum,  the  pulp  of 
an  apple,  grains  of  wheat. 

After  the  above  substances  have  been  thoroughly  dried  and 
weighed,  immerse  them  in  water  for  one  hour,  wipe  them  as  dry 
as  possible  by  means  of  blotting-paper,  and  weigh  again.  How 
much  water  can  each  absorb  in  one  hour?  In  like  manner  as- 
certain how  much  the}-  will  absorb  in  ten  hours  and  in  twenty- 
four  hours. 


RELATIONS  OP  THE  PLANT  TO  WATER.  25 


VI.  ROOT-ABSORPTION. 
Repeat  the  following  experiments  by  Ohlert :  — 

Cut  off  the  so-called  spongioles,  the  very  tips  of  the  roots  of 
sound  seedlings  which  have  been  cultivated  for  a  few  days  upon 
moist  sand  or  sponge  (or,  better  still,  with  all  the  roots  in  water), 
and  cover  the  wounds  with  asphalt-varnish.  The  wounded  end 
of  the  root  must  be  quickly  dried  with  blotting-paper  before  the 
varnish  is  applied.  Then  put  the  roots  of  the  plant  again  upon 
their  moist  support  or  in  water,  and  endeavor  to  answer  by  care- 
ful observation  the  question  :  Does  or  does  not  the  plant  absorb 
enough  water  for  its  needs  without  the  "  spongioles"? 

Cultivate  seedlings  of  one  or  two  plants,  for  instance  radish 
and  wheat,  upon  (1)  rather  dry  sand ;  (2)  moist  sand ;  (3)  wet 
sand,  or  upon  blotting-paper  of  these  three  degrees  of  moisture, 
and  notice  if  there  is  any  appreciable  difference  in  the  number  of 
root-hairs  produced.  Can  the  development  of  the  hairs  be  in- 
creased by  increasing  slightly  the  temperature  of  the  support? 

VII.  ROOT  PRESSURE. 

Cut  off  square!}-  the  stem  of  a  young  dahlia  or  sunflower  well 
rooted  in  a  flower-pot  of  moderate  size,  and  to  the  stump  fasten 
immediately  a  T-tube,  with  its  pressure-gauge  as  directed  on 
page  264.  Ascertain  the  pressure  shown  by  the  mercurial  gauge 
at  intervals  of  an  hour,  and  determine  also  the  effect  of  chang- 
ing the  temperature  of  the  soil  in  the  flower-pot. 

VIII.    STEM  PRESSURE. 

Apply  a  pressure-gauge  to  the  cut  stem  of  some  woody  plant 
well  established  in  a  flower-pot  (for  instance,  a  strong  rose),  and 
ascertain  the  amount  of  pressure  exerted  by  the  sap. 

In  the  winter  time  or  early  spring  try  the  experiments  referred 
to  on  pages  264-267. 

IX.     TRANSFER  OF  WATER  THROUGH  STEMS. 

Repeat  De  Vries's  experiments  described  on  page  263.  For 
these,  stems  of  sunflower  and  tobacco  answer  very  well,  while 
those  of  heliotrope  are  not  very  good.  Ascertain  the  height  to 
which  a  color  (as  anilin  red)  will  rise  in  the  cut  stern  of  a  young 
woody  plant  under  different  conditions  of  warmth,  exposure  of 
the  leaves  to  light,  etc.  Repeat  the  experiment  with  a  strip 
of  blotting-paper,  described  on  page  260.  Try  the  foregoing 


26  STUDIES   IN  HISTOLOGY. 

with  the  substitution  of  a  salt  of  lithium  for  the  dj-e,  and  deter- 
mine the  rate  of  ascent. 

It  will  be  well  for  the  student  at  this  point  to  review  carefully 
the  principal  facts  regarding  the  amount  of  moisture  which  the 
atmosphere  can  take  up  at  different  temperatures.  In  all  trans- 
piration experiments  he  should  determine  the  percentage  of 
moisture  in  the  atmosphere  to  which  the  leaves  of  the  plants 
are  exposed,  and  for  this  purpose  the  well-known  Hygrodeik, 
or  Hygrophant,  may  be  employed.  But  if  only  the  simple  wet 
and  dry  thermometer  bulbs  are  at  hand,  the  student  can  find 
all  necessary  data  for  his  calculations  in  the  tables  published  by 
the  Smithsonian  Institution. 

Place  in  a  watch-glass  under  the  microscope  water  containing 
finely  powdered  indigo,  and  immerse  in  it  the  clean-cut  surface 
of  a  leafy  shoot.  Observe  in  which  direction  the  indigo  particles 
move. 

X.    TRANSPIRATION,  OR  EXHALATION. 

Repeat  the  following  experiment  devised  by  Henslow :  "  Take 
six  or  eight  of  the  largest,  healthiest  leaves  you  can  find,  two 
tumblers  filled  to  within  an  inch  of  the  top  with  water,  two 
empty  dry  tumblers,  and  two  pieces  of  card  each  large  enough 
to  cover  the  mouth  of  the  tumbler.  In  the  middle  of  each  card 
bore  three  or  four  small  holes  just  wide  enough  to  allow  the 
petiole  of  a  leaf  to  pass  through.  Let  the  petioles  hang  suffi- 
ciently deep  in  the  water  when  the  cards  are  put  upon  the  tum- 
blers containing  it.  Having  arranged  matters  thus,  turn  the 
empty  tumblers  upside  down,  one  over  each  card,  so  as  to  cover 
the  blade  of  the  leaves.  Place  one  pair  of  tumblers  in  the  sun- 
shine, the  other  pair  in  a  shady  place.  In  five  or  ten  minutes 
examine  the  inverted  tumblers." 

Tie  a  piece  of  thin  rubber-cloth  around  the  flower-pot  and 
lower  part  of  the  stem  of  any  young  leafy  plant,  and  weigh  the 
whole  upon  a  common  balance  capable  of  turning  with  a  deci- 
gram, under  a  lead  of  two  or  three  kilograms.  If  nothing  better 
can  be  procured,  one  of  the  best  forms  of  small  platform  balance 
will  answer.  A  thistle-funnel  should  be  tied  up  with  the  stem, 
so  that  water  can  be  supplied  to  the  plant  as  required.  Ascer- 
tain the  amount  of  transpiration  from  the  foliage  of  the  plant 
during  twenty-four  hours  under  the  following  conditions:  (1)  at 
a  temperature  not  falling  below  60°  F.  (about  16°  C.) ;  (2)  at  a 
temperature  not  rising  above  40°  F.  (about  4°  C.). 

What  is  the  loss  of  moisture  in  one  hour  under  direct  exposure 
to  the  brightest  sunlight?  Note  temperature  and  moisture  in  the 


ASH  OF  PLANTS.  27 

air.  What  is  the  effect  upon  transpiration  of  placing  the  flower- 
pot in  some  crushed  ice,  the  temperature  of  the  air  remaining 
about  the  same  as  before  ? 

Determine  the  minimum,  maximum,  and  optimum  temperature 
for  transpiration  of  any  suitable  herbaceous  plant,  for  example, 
a  Pelargonium  (House  Geranium). 

XI.   EXTRAVASATION  FROM  LEAVES. 

Cover  a  young  healthy  plant  of  Indian  corn  or  wheat  with  a 
bell-jar,  being  careful  to  keep  it  warm.  If,  after  a  little  time, 
a  drop  of  water  should  appear  at  the  tip  of  any  of  the  leaves, 
remove  it  by  blotting-paper,  and  replace  the  bell-jar.  What  is 
the  lowest  temperature  at  which  water  is  thus  given  off  by  young 
leaves  of  the  above  plants  ? 

If  a  young  Caladium  is  at  hand,  examine  the  tip  of  the  leaf 
for  the  jet  of  water  (page  268)  which  can  sometimes  be  seen. 
If  the  plant  is  a  suitable  one,  and  the  jet  can  be  seen  at  all, 
ascertain  the  lowest  temperature  at  which  it  is  ejected. 

XII.  INCOMBUSTIBLE  MATTERS  IN  THE  PLANT. 

Burn  upon  platinum  foil  (free  access  of  air  being  permitted), 
known  weights  of  the  following  substances,  and  weigh  the  ash 
left  in  each  case:  (1)  oak-wood,  (2)  pine-wood,  (3)  a  young 
leaf  of  any  plant,  (4)  a  much  older  leaf  of  the  same  plant  (for 
instance  raspberry),  and  (5)  some  grains  of  Indian  corn. 

If  no  platinum  foil  is  at  hand,  burn  the  substance  in  a  hard 
glass  tube  open  at  both  ends  and  held  slightly  inclined  in  the 
flame  of  an  alcohol  lamp  or  of  a  Bunsen  burner.  If  the  glass 
tube  is  used  instead  of  platinum  foil,  weigh  the  tube  and  the 
substance  together  before  heating,  and  afterwards  weigh  tube 
and  ash  together  to  obtain  the  difference  in  weight. 

XIII.  EXAMINATION  OF  THE  ASH  or  PLANTS. 

If  the  student  has  facilities  for  conducting  qualitative  chemical 
analyses,  he  would  do  well  to  examine  the  ash  of  the  following 
plants  :  Sugar-beet,  Buckwheat,  and  Oat. 

If  he  has  had  sufficient  practice  in  quantitative  chemical 
analysis  to  warrant  it,  an  examination  of  the  ash  of  some  one 
of  the  plants  which  have  been  spoken  of  in  664  and  665  would 
form  a  useful  exercise.  The  investigation  of  the  ash  of  a  single 
species  at  different  seasons  is  recommended. 


28  STUDIES   IN    PHYSIOLOGY. 


XIV.    WATER-CULTURE. 

In  the  study  of  water-culture  no  plants  can  be  more  easily 
managed  than  buckwheat  and  Indian  corn.  Secure  good  seed- 
lings, and  treat  them  as  described  in  669.  After  the  plants 
have  become  well  established  in  their  new  surroundings,  use  for 
the  nutrient  liquid  the  following  solutions  in  a  fixed  order,  and 
with  the  precautions  laid  down  on  page  249. 

1.  Well- water,  or  other  drinking-water. 

2.  Distilled  water  with  potassic  nitrate. 

3.  "  "  "          "       chloride. 

4.  "  **  "  magnesic  sulphate. 

5.  "  "  "  calcic  chloride. 

6.  "  "  "        "     sulphate. 

7.  "  "  «*  potassic  phosphate. 

8.  Nutrient  solution   I.  (672). 

9.  »  "       II.  (673). 

10.  Distilled  water  alone. 

XV.    ASSIMILATION  PROPER. 

Chlorophyll  and  other  coloring-matters.  Make  a  solution  of 
the  pigment  by  placing  bruised  leaves  of  grass  in  strong  alcohol 
for  a  few  hours,  and  keeping  them  from  the  light.  It  is  well  to 
prepare  at  least  ten  ounces  of  the  strong  extract,  which  can  be 
used  in  all  the  following  experiments. 

Examine  the  color  of  about  an  ounce  of  the  above  extract  held 
in  a  small  vial.  "What  is  its  color  by  transmitted  and  by  re- 
flected light?  In  the  latter  examination  it  is  better  to  throw  a 
strong  light  from  a  burning-glass  or  double  convex  lens  upon  the 
surface  of  the  liquid.  How  long  will  the  liquid  keep  its  color  in 
the  strong  light? 

Treat,  as  directed  in  774,  one  ounce  of  the  extract  which  has 
not  been  exposed  to  light,  and  place  the  turbid  mixture  aside  in 
a  dark  place  until  it  becomes  clear.  What  are  the  colors  of  the 
upper  and  the  lower  layer  into  which  it  separates? 

If  a  microspectroscope  is  available,  make  on  paper  projections 
of  the  spectra  of  the  following  substances  :  (1)  Chlorophyll  solu- 
tion, (2)  the  upper  layer  of  the  liquid  just  mentioned,  and  (3) 
the  lower  layer  of  the  lir^iid.  Examine  also  the  spectrum  of  a 
thin  green  leaf. 

If  possible,  examine  the  colors  of  autumnal  leaves,  and  of 
alcoholic  extracts  from  colored  flowers  and  colored  fruits. 


ASSIMILATION.  29 

Place  a  few  red  sea-weeds  in  pure  water,  and  let  them  remain 
there  for  ten  hours.  What  is  the  color  of  the  water  by  (1)  trans- 
mitted light?  (2)  by  reflected  light?  Extract  the  coloring-matter 
of  red  sea-weeds  by  means  of  alcohol,  and  compare  the  alcoholic 
with  the  aqueous  solution. 

What  is  the  color  of  an  alcoholic  extract  of  the  bruised  tissues 
of  Monotropa  uniflora  ? 

Etiolation.  Keep  seedlings  in  a  warm,  dark  place  until  they 
have  lost  their  green  color,  and  then,  having  removed  some  of 
their  leaves  for  immediate  examination,  place  the  plants,  with  the 
remaining  leaves  attached,  in  the  light.  Make  alcoholic  extracts 
of  the  blanched  leaves  and  of  the  green  ones,  comparing  them 
from  all  points  of  view. 

Examine  pine  seedlings  grown  in  complete  darkness,  and  ascer- 
tain the  nature  of  the  pigment  which  their  green  cells  contain. 

Carbonic  acid  and  assimilation.  Compare  at  the  end  of  two 
or  three  weeks  the  dry  weights  of  two  seedlings  grown  under  the 
following  conditions :  Both  the  seedlings  have  furnished  to  them 
exactly  the  same  kind  and  amount  of  soil,  and  are  provided  with 
equal  amounts  of  nutrient  solutions  at  corresponding  times ; 
both  are  placed  under  tubulated  bell-jars,  and  have  the  same 
amount  of  moisture  in  the  atmosphere  to  which  the}-  are  exposed. 
The  seedling  in  one  bell-jar  obtains  a  supply  of  carbonic  acid 
gas,  since  there  is  an  opening  in  the  jar  through  which  the  en- 
closed air  communicates  with  that  outside  containing  its  normal 
proportion  of  carbonic  acid.  The  seedling  in  the  other  jar  has 
no  carbonic  acid  supplied,  since  a  cup  which  contains  potas- 
sic  hydrate  deprives  the  air  already  in  the  jar  of  all  its  carbonic 
acid,  and  an  open  receptacle,  filled  with  pumice-stone  satu- 
rated with  potassic  h^'drate,  removes  all  carbonic  acid  from 
any  air  entering  the  jar.  One  plant  is  thus  furnished  with 
enough  available  carbonic  acid,  the  other  is  in  an  atmosphere 
wholly  free  from  it. 

In  a  modification  of  the  foregoing  experiment,  supply  a  known 
quantity  of  carbonic  acid  in  aqueous  solution  to  the  soil  of  the 
second  plant,  being  careful  to  prevent  by  means  of  a  cover  of 
rubber-cloth  any  escape  of  the  carbonic  acid  from  the  soil  of  the 
flower-pot  into  the  air  of  the  jar,  and  after  a  few  days  compare 
the  weights  of  the  plants  as  before. 

Can  a  water  plant  derive  its  carbonic  acid  from  water  contain- 
ing a  small  amount  of  sodic  bicarbonate  in  solution  ? 

Add  to  the  normal  air  contained  in  a  freshly  filled  bell-jar,  in 
which  a  seedling  is  growing,  a  known  quantity  of  pure  carbonic 


30  STUDIES   IN   PHYSIOLOGY. 

acid.1  Later,  double  and  quadruple  the  quantity  added,  and 
observe  the  effect  produced  upon  the  plant.  Experiment  with 
different  species  of  ferns  and  club  mosses  in  the  same  manner. 
Observe  in  another  series  of  experiments  the  effect  of  sunlight 
in  modifying  the  influence  of  an  excess  of  carbonic  acid  gas  in 
the  atmosphere. 

The  measure  of  assimilative  activity  is  to  be  found  either 
in  the  amount  of  pure  oxygen  evolved  in  assimilation,  or  in  the 
amount  of  carbonic  acid  decomposed  in  it. 

1.  Determinations   depending   upon   the  amount  of  oxygen 
evolved :  The  gas  which  is  given  off  during  assimilation,  espe- 
cially by  water  plants,  is  never  absolutely  pure  oxygen  ;    but 
since  it  contains  so  small  a  proportion  of  other  matters  under 
most   circumstances  which   the   student  is  likely  to  meet,  the 
amount  of  it  evolved  may  be  taken  safely  as  the  approximate 
measure  of  assimilation.     The  method  of  measurement  by  count- 
ing bubbles  emitted  by  water  plants  in  water  (see  814)  is  always 
practicable  and  easy  of  execution.     The  evolved  g£s  can  be 
easily  collected  in  any  convenient  inverted  receptacle.    If  the  gas 
collected  and  measured  is  analyzed  eudiometrically,  as  d'v  )cted 
in  Bunsen's  "Gasometry,"  the  determination  leaves  little  to  be 
desired. 

2.  Determinations  depending  upon  the  amount  of  carbonic 
acid  decomposed.    To  the  air  contained  in  a  glass  vessel  in- 
verted over  mercury  a  known  quantity  of  carbonic  acid  is  added. 
The  plant  previously  placed  in  the  receptacle  decomposes  a  part 
of  this,  and  after  a  given  time  the  amount  decomposed  is  ascer- 
tained by  measurement  of  the  carbonic  acid  that  remains. 

Effects  of  different  gases  upon  assimilation.  A  few  plants 
and  two  or  three  small  Wardian  cases,  or,  better,  capacious  bell- 
jars,  will  answer  for  this  study.  Select  only  sound  plants  for 
examination,  and  be  careful  to  have  those  in  one  bell-jar  as  nearly 
as  possible  of  the  same  size  and  strength  as  those  in  the  others. 
Let  the  air  in  one  of  the  jars  be  ordinary  atmospheric  air ;  to  that 
in  the  others  add  a  known  but  small  quantity  of  one  of  the  fol- 
lowing gases  :  namely,  (1)  common  coal  gas  ;  (2)  sulphurous  acid  ; 
(3)  chlorine.  Compare  the  growth  and  vigor  of  the  plants  from 
time  to  time,  and  observe  whether  insolation  makes  any  difference 
in  the  appearance  of  the  plants  exposed  to  the  gases  mentioned. 

1  In  all  cases  where  an  additional  amount  of  gas  is  introduced  into  a  bell- 
jar,  allowance  must  be  made  in  some  way  for  the  possible  increase  of  pressure. 
For  the  necessary  correction  in  these  cases,  and  for  other  details  regarding  the 
management  of  gases,  consult  Bunsen's  "Gasometry." 


RESPIRATION.  31 


XVI.    RESPIRATION. 

The  measure  of  this  process  is  usually  found  in  the  amount 
of  carbonic  acid  given  off  by  plants.  The  methods  of  deter- 
mination of  this  amount  are,  although  apparently  simple,  open 
to  some  objections ;  but  by  the  exercise  of  great  care  in  the 
management  of  the  simple  appliances,  their  results  are  in  gen- 
eral trustworthy. 

The  carbonic  acid  which  is  given  off  by  the  plant  may  be 
measured  in  one  of  the  two  following  ways :  (1)  A  current  of 
air  freed  from  all  its  carbonic  acid  by  means  of  wash-bottles  con- 
taining potassic  hydrate  is  allowed  to  pass  into  a  receptacle  in 
which  are  confined  the  plants  to  be  examined.  The  air  with- 
drawn from  this  receptacle  passes  slowly  through  Liebig's  potash 
bulbs  in  which  are  held  a  known  amount  of  potassic  hydrate. 
At  the  conclusion  of  the  observation  the  amount  of  carbonic  acid 
which  has  been  given  off  by  the  plants  and  been  taken  up  by  the 
potassic  hydrate  in  the  bulbs  can  be  accurately  determined. 
(2)  The  current  of  air  which  is  withdrawn  from  the  receptacle 
containing  the  plant  is  permitted  to  pass  very  slowly  through  a 
long  slightly  inclined  tube  in  which  is  held  a  solution  of  pure 
baric  hydrate.  As  the  bubbles  of  gas  pass  through  this  liquid 
and  give  up  their  carbonic  acid,  they  cause  an  abundant  precipi- 
tation of  baric  carbonate  in  it.  The  second  method,  which  is 
essentially  that  of  Pettenkofer,  yields  uniform  results,  and  is 
in  general  to  be  preferred  to  the  first.  It  is  better  applicable 
to  observations  upon  intramolecular  respiration ;  in  which,  as 
pointed  out  in  981,  some  gas  like  nitrogen  or  hydrogen,  wholly 
free  from  any  trace  of  oxygen,  is  allowed  to  come  in  contact  with 
plants  or  parts  of  plants,  and  the  amount  of  carbonic  acid  given 
off  is  determined  as  in  the  former  case.  Interesting  results  are 
obtained  by  placing  in  the  receptacle  very  young  seedlings,  or 
buds  which  have  just  begun  to  unfold. 

XVII.    GBOWTH. 

The  measnrement  of  growth.  Growth  can  be  satisfactorily 
measured  in  the  three  following  ways,  each  of  which  is  adapted 
to  particular  instances  :  — 

1.  Direct  measurement.  Determine  the  place  and  rate  of 
growth  of  young  internodes  of  any  rapidly  developing  plant,  for 
instance  Morning  Glory,  by  marking  the  whole  space  of  the 
internodes  into  equal  intervals,  and  subsequently  determining 


32  STUDIES   IN   PHYSIOLOGY. 

the  actual  increase  in  distance  between  any  two  or  more  lines. 
In  all  cases  mark  the  part  under  examination  with  good  India- 
ink,  making  clear,  narrow  lines.  To  avoid  any  possible  error 
caused  by  influence  of  lines  marked  only  on  one  side,  make 
lines  on  both  sides  of  a  part  whenever  possible.  To  measure 
the  growth  of  leaves,  use  the  method  spoken  of  on  page  156. 

2.  Measurement  by  a  micrometer  eye-piece.     With  the  tube 
of  the  microscope  kept  perfectly  horizontal,  examine  the  position 
of  a  line  of  India-ink,  upon  a  perianth  leaf  of  Crocus,  or  upon 
the  root-cap  of  Windsor  bean.     Observe  the  space  which  the 
image  of  the  line  appears  to  pass  through  in  a  given  time,  and 
refer  this  to  the  previously  determined  values  of  the  spaces  of 
the  micrometer. 

3.  Measurement  by  an  index,   (a)  On  a  simple  arc.     For 
this  use  the  simple  and  admirable  modification  of  Sachs's  aux- 
anometer,  devised  by  Bessey  (American  Naturalist). 

(b)  On  a  recording  drum.  A  slender  brass  or  steel  shaft  is 
attached  to  the  hour-spindle  of  a  cheap  clock,  and  from  the  shaft 
is  suspended  firmly  a  stiff  pasteboard  drum  of  about  the  same 
size.  This  revolves  with  the  spindle,  and  if  well  made  is 
carried  without  any  appreciable  vibration.  A  piece  of  glazed 
paper  of  the  size  of  the  drum  is  moistened,  and  a  little  mucilage 
placed  on  one  edge,  so  that  when  the  paper  is  rolled  around  tho 
drum,  its  edges  can  be  firmly  fastened  together.  Be  careful  to 
have  the  seam  in  the  paper  so  placed  as  to  avoid  any  catching 
of  the  needle  index  attached  to  the  plant.  When  the  paper  on 
the  drum  is  dry,  it  is  smoked  lightly  and  evenly  over  a  smoky 
turpentine  flame.  The  needle  at  the  tip  of  the  index  is  now 
placed  against  the  smoked  paper  so  as  to  press  lightly  upon  it, 
and,  as  the  drum  revolves,  leave  a  clean  mark.  When  a  suffi- 
ciently long  record  has  been  registered,  the  paper  is  carefully 
removed  and  dipped  in  (not  brushed  with)  a  solution  of  common 
rosin  in  alcohol,  which  upon  drying  prevents  any  of  the  lamp- 
black from  coming  off. 

Two  corrections  are  necessary  with  this  simple  apparatus  : 
(1)  for  the  curve  of  the  descending  needle  at  the  end  of  the 
radius ;  (2)  for  any  changes  in  the  position  of  the  needle  caused 
by  the  varying  amount  of  moisture  in  the  air. 

For  recording  temperature,  it  is  possible  to  use  a  metallic 
thermometer  with  a  long  index,  and  have  the  two  records  side 
by  side.  It  is  well,  however,  to  have  the  needle  for  the  ther- 
mometer give  a  different  mark  in  order  to  prevent  any  subsequent 
confusion. 


MOVEMENTS   OP   PLANTS.  33 

The  proper  methods  of  examining  the  formation  of  new  cells 
in  a  simple  case  are  indicated  in  the  studies  upon  a  stamen-hair 
of  Tradescantia  noted  on  page  380. 

XVIII.    MOVEMENTS  OF  PLANTS. 

The  student  is  advised  to  select  some  one  plant  in  a  vigorous 
condition  and  make  a  thorough  examination  of  all  the  phenomena 
of  movement  which  it  presents.  The  plants  named  below  are 
among  the  best  for  such  an  examination,  and  they  can  be  made 
to  grow  even  under  rather  unfavorable  conditions,  like  those 
afforded  by  schoolrooms. 

Spontaneous  movements.  Desmodium  gyrans,  the  Morning 
Glory,  or  Hop,  may  be  used.  The  first  requires  a  high  tem- 
perature and  a  fair  amount  of  moisture  in  the  air  in  order  to 
exhibit  its  peculiar  movements  satisfactorily. 

Movements  following  shock.  The  Sensitive  plant  (Mimosa 
pudica)  should  be  observed.  It  can  be  experimented  upon  with 
various  kinds  of  irritants,  both  mechanical  and  chemical,  at 
various  temperatures,  and  under  the  influence  of  anaesthetics. 
For  the  experiments  with  anaesthetics  only  very  young  plants 
are  suitable,  and  they  cannot  well  be  used  afterwards  for  other 
investigations. 

In  the  case  of  all  of  the  above  plants  note  any  changes  which 
the  leaves  undergo  during  the  day  and  at  the  approach  of 
night. 

The  details  given  in  1045  suffice  to  indicate  the  general  method 
of  exaggerating  by  means  of  slender  glass  threads  the  slow  and 
slight  movements  of  plants,  and  do  not  need  further  treatment 
here.  For  observations  with  such  threads,  the  following  plants 
are  very  useful :  seedlings  of  the  Morning  Glory,  clover,  cress, 
cabbage,  and  sunflower. 

XIX.   TENSION  OF  TISSUES. 

Make  sections  of  young  internodes  as  directed  in  1025,  secur- 
ing in  every  case  accurate  measurements  of  all  the  parts,  both 
before  and  after  their  separation.  It  will  be  well  to  examine  in 
like  manner  a  large  number  of  young  roots,  stems,  leaves,  and 
parts  of  flowers,  noting  in  all  cases  the  age  of  the  part  examined. 

XX.    INSECTIVOROUS  PLANTS. 

In  the  study  of  these  plants  the  student  is  advised  to  read 
carefully  Mr.  Darwin's  work  on  the  subject,  and  verify,  by  means 


34  STUDIES   IN   PHYSIOLOGY. 

of  good  specimens  of  Drosera  rotundifolia,  the  facts  there  re- 
corded. Students  are  reminded  that  Mr.  Darwin's  observations 
were  made  with  the  simplest  appliances,  and  with  a  degree  of 
care  never  excelled. 

For  independent  study  abundant  material  may  be  found  in  the 
common  Sarracenias  of  the  North  and  South,  in  regard  to  which 
very  much  still  remains  to  be  learned. 

XXI.   CROSS-FERTILIZATION. 

For  this  study,  repeat  the  observations  of  Darwin  as  the}* 
are  given  in  his  work  on  Cross  and  Self  Fertilization  ;  or  if  that 
is  not  at  hand,  as  they  are  briefly  stated  in  the  abstract  in  the 
present  volume,  pages  448-450. 

XXII.  HYBRIDIZING. 

With  the  precautions  given  on  page  456  the  student  should 
be  able  to  undertake  experiments  in  hybridizing  species  of  the 
following  common  genera,  all  of  which  lend  themselves  readily 
to  this  process :  Nicotiana,  Verbascum,  Lilium,  etc.  Be  care- 
ful to  exclude  foreign  pollen  in  all  cases. 

XXIII.   THE  RIPENING  or  FRUITS  AND  SEEDS. 

Good  material  for  this  study  is  afforded  by  the  following 
plants :  Solanum,  Impatiens,  PJTUS,  Prunus,  and  Tecoma. 

XXIV.   GERMINATION. 

Select  sound  seeds  of  some  common  plant,  for  instance  beans 
or  Indian  corn,  and  test  with  them  the  truth  of  the  following 
statements:  (1)  Water  is  essential  to  germination.  (2)  Germi- 
nation cannot  begin  without  access  of  free  oxygen.  (3)  Seeds 
of  the  plants  selected  require  the  same  temperature  for  the  be- 
ginning of  germination.  (4)  When  the  process  of  germination 
has  once  begun,  light  is  necessary  to  any  increase  of  the  plant  in 
dry  substance  (compare  experiment  Series  1,  No.  II.).  (5)  Car- 
bonic acid  is  constantly  given  off  during  germination.  (6)  In 
some  cases  carbonic  acid  will  continue  to  be  evolved  even  when 
no  more  oxygen  is  supplied  (compare  intramolecular  respira- 
tion). (7)  The  temperature  of  germinating  seeds  is  higher  than 
that  of  the  surrounding  atmosphere  (compare  respiration). 

What  is  the  optimum  amount  of  water  required  for  the  speedy 
germination  of  the  following  seeds,  — Windsor  beans,  peas, 
clover,  squash,  and  sunflower? 


EFFECTS   OF   FKOST.  35 

What  is  the  optimum  amount  of  oxygen  required? 

What  is  the  optimum  temperature  required  ? 

Compare  the  precocity  of  unripe  and  ripe  seeds  of  any  plant. 

XXV.   EFFECTS  OF  FROST. 

Wrap  up  a  leaf  of  Begonia  in  thin  rubber-cloth,  to  protect  it 
from  moisture,  and  place  it  in  a  freezing  mixture  of  powdered 
ice  and  salt.  After  an  hour  examine  the  tissues  of  the  leaf  with 
special  reference  to  any  mechanical  injury  which  they  may  have 
sustained.  Having  completed  this  preliminary  study,  proceed 
to  the  examination  of  any  well-developed  seedlings,  and  note  in 
every  case  (1)  the  effect  produced  upon  the  parts  which  have 
been  quickly  thawed;  (2)  the  effect  where  thawing  has  been 
allowed  to  go  on  very  slowly. 

Freeze  any  strong  seedlings  and  after  a  time  thaw  them 
slowly.  Place  them  then  under  favorable  conditions  for  growth, 
in  order  to  ascertain  whether  their  vitality  has  been  destroyed. 
In  cases  where  death  of  the  part  or  plant  ensues,  does  it  appear 
to  come  from  the  freezing  or  from  the  thawing? 


TABLE  OF   MEASURES. 


MEASURES  OF  LENGTH. 

Inches. 

Meter  ;     39.37079 

Millimeter   ....                                                                    003937 

Micro-millimeter  (/*)  the  unit  of  microscopic  measurement  .    0.000039 

MEASURES  OF  CAPACITY. 

Pints.             Cubic  Inches. 

Liter  1  761               61  02705 

Cubic  centimeter  or  milliter     .    .         .         .       00176    .         006103 

MEASURE  OF  WEIGHT. 

Grains. 

Gram  .         .     .                                                                           1543235 

MEASURES  OF  TEMPERATURE. 

Centigrade, 

or  Celsius. 

Fahrenheit. 

Rewnur. 

Centigrade, 
or  Celsius. 

Fahrenheit. 

Remmur 

o 

0 

o 

0 

o 

0 

+100 

+212 

+80 

+  16 

+60.8 

+12.8 

90 

194 

72 

15 

69 

12 

80 

176 

64 

14 

57.2 

11.2 

70 

158 

56 

13 

55.4 

10.4 

60 

140 

48 

12 

63.6 

9.6 

60 

122 

40. 

11                61.8 

8.8 

49 

120.2 

89.2 

10                 60 

8 

48 

118.4 

38.4 

9                 48.2 

7.2 

47 

116.6 

87.6 

8                 46.4 

6.4 

46 

114.8 

36.8 

7                 44.6 

6.6 

45 

113 

36 

6                 42.8 

4.8 

44 

111.2 

36.2 

6 

41 

4 

43                 109.4 

34.4 

4 

39.2 

3.2 

42                107.6 

as.6 

3                 37.4 

2.4 

41 

105.8 

32.8 

2                 35.6 

1.6 

40 
39 

104 
102.2 

32 
31.2 

+i 

+33.8 
+32 

+0.8 
0 

38 

100.4 

30.4 

—1 

+30.2 

—0.8 

37 

98.6 

29.6 

2 

28.4 

1.6 

36 

96.8 

28.8 

3 

26.6 

2.4 

35 

95 

28 

4 

24.8 

3.2 

34 

93.2 

27.2 

6 

23 

4 

33 

91.4 

26.4 

6 

21.2 

4.8 

32 

89.6 

25.6 

7 

19.4 

6.6 

31 

87.8 

24.8 

8 

17.6                 6.4 

30 

86 

24 

9 

16.8 

7.2 

29 

84.2 

23.2 

10 

14 

8 

28 

82.4 

22.4 

11 

12.2 

8.8 

27 

80.6 

21.6 

12 

10.4 

9.6 

26 

78.8 

20.8 

13 

8.6 

10.4 

25 

77 

20 

14 

6.8 

11.2 

24 

75.2 

19.2 

16 

6. 

12 

23 

73.4 

18.4 

16 

3.2 

12.8 

22 

71.6 

17.6 

17 

1.4 

13.6 

21 

69.8 

16.8 

18 

—0.4 

14.4 

20 

68 

16 

19 

2.2 

15.2 

19 

66.2 

15.2 

20 

4 

16 

18 

64.4 

14.4 

80 

22 

24 

17 

62.6 

13.6 

—40 

—40 

—32 

?* 


THE  LIBRARY 
UNIVERSITY  OF  CALIFORNIA 

Santa  Barbara 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW. 


30w-9,'66(GG33888)iM8i! 


